Add planning baseline: BC, SA, PP and two gateways

Create the Business Case, Stakeholder Analysis (S01 course participant,
S02 Udemy coursists, S03 GitHub viewers), Project Plan and the milestone
documents MIL-001 (project setup, 6 tasks) and MIL-002 (game
implementation, 8 tasks) for the console Blackjack game.

Register PP and MIL in the artifact registry, set the PO language to en,
and link the synced Gitea milestones in the Gateway Schedule.

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.agents/skills/coding-conventions/references/c.md

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+# C conventions
+
+C has no single official style guide. This sub-skill fixes one consistent
+style built on common practice; MISRA C and SEI CERT C are the references for
+safety-critical or security-sensitive code.
+
+## Standard base
+
+ISO C11 or C17 as set by the project's compiler flag (`-std=c11`). Compile
+with warnings on (`-Wall -Wextra -Wpedantic`); treat warnings as errors in
+release builds.
+
+## Naming
+
+| Element | Convention | Example |
+| --- | --- | --- |
+| Function, variable, parameter | `snake_case` | `parse_header`, `byte_count` |
+| Public symbol | module prefix plus `snake_case` (C has no namespaces) | `stay_reader_open()` |
+| File-local function / variable | `static`, no prefix needed | `static int next_token(...)` |
+| Type (`struct`, `enum`, `typedef`) | `snake_case_t`, module prefix for public types | `stay_reader_t` |
+| Enum constant, macro, constant | `UPPER_SNAKE` with the module prefix | `STAY_READER_OK` |
+| Header / source file | `snake_case.h` / `snake_case.c`, same base name | `stay_reader.h` |
+| Header guard | `MODULE_FILE_H` (or `#pragma once` if the project allows) | `STAY_READER_H` |
+
+- Do not use reserved identifiers: a leading underscore followed by an
+  uppercase letter, any double underscore, or a leading underscore at file
+  scope.
+- POSIX reserves the `_t` suffix; keep the module prefix on public types so
+  they cannot collide.
+- Macros are a last resort; prefer `static inline` functions and `enum` or
+  `const` values.
+
+## Formatting
+
+- One formatter configuration for the project (`clang-format`); 4 spaces (or
+  the project's setting), no tabs mixed in.
+- Braces on every `if`, `else`, `for`, `while`, even for one statement.
+- One declaration per line; declare variables at first use, initialised.
+- Headers: include what you use, only what you use; public headers are
+  self-contained; add `extern "C"` guards when C++ code consumes them.
+
+## Language rules
+
+- Check every return value that can fail; check every allocation.
+- Every `malloc`/`open`/`lock` has one clear owner and one matching release;
+  release on every exit path (single exit or `goto cleanup`).
+- Use `size_t` for sizes and indices, fixed-width types (`<stdint.h>`) for
+  data layout, `const` wherever data is not modified, `restrict` only with
+  care.
+- Bounds are explicit: pass a length with every buffer; use `snprintf`,
+  never `sprintf`, `strcpy` or `gets`.
+- No undefined behaviour: no signed overflow, no out-of-range shifts, no use
+  after free, no uninitialised reads.
+- Avoid global mutable state; if unavoidable, `static` and documented.
+
+## Errors
+
+Return a status code (an `enum`) or `-1`/`NULL` plus an error out-parameter;
+document which in the header. Never ignore a failing call. Read `errno`
+immediately after the failing call.
+
+## Tests
+
+A unit-test framework (for example Unity or CMocka); run under sanitizers
+(`-fsanitize=address,undefined`) in at least one build.
+
+## Tooling
+
+`clang-format`, `clang-tidy` or `cppcheck`, compiler warnings, sanitizers.
+
+Review with `QC-CL-001`.

.agents/skills/coding-conventions/references/cpp.md

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+# C++ conventions
+
+## Standard base
+
+ISO C++17 or later as set by the project (`-std=c++20`); the C++ Core
+Guidelines are the rule source. C++ has no official naming style, so the
+style below is used unless the project already has another (rule 1 of the
+overall skill).
+
+## Naming
+
+| Element | Convention | Example |
+| --- | --- | --- |
+| Class, struct, enum, concept, type alias | `PascalCase` | `StayReader`, `Stay` |
+| Function, method, variable, parameter | `snake_case` | `read_stays()`, `byte_count` |
+| Data member (private) | `snake_case` with trailing underscore | `buffer_` |
+| Struct public data member | `snake_case`, no underscore | `check_in` |
+| Constant (`constexpr`, namespace-scope `const`) | `kPascalCase` | `kMaxRetries` |
+| Enum class value | `PascalCase` | `Status::NotFound` |
+| Namespace | short `snake_case`; no `using namespace` in headers | `billing` |
+| Template parameter | `PascalCase` | `typename ItemT` |
+| Macro | `UPPER_SNAKE` with project prefix; avoid macros | `BILLING_ASSERT` |
+| Header / source file | `snake_case.h` / `snake_case.cpp`, same base name | `stay_reader.h` |
+| Header guard | `#pragma once` (or `PROJECT_PATH_FILE_H`) | |
+
+## Formatting
+
+- `clang-format` with one checked-in config; 4 spaces (or the project's
+  setting); braces on every control-flow body.
+- Include order: matching header, project headers, third party, standard
+  library; each group sorted.
+- One declaration per line; declare at first use, initialise with `{}`.
+
+## Language rules
+
+- **Ownership:** RAII everywhere. No owning raw pointers, no naked
+  `new`/`delete`; use `std::unique_ptr` by default, `std::shared_ptr` only for
+  real shared ownership, created with `std::make_unique`/`make_shared`.
+- Follow the rule of zero; if you define one of destructor, copy or move,
+  define or delete all five.
+- Pass by `const&` (large, read-only) or by value (small or sink); use
+  `std::span` and `std::string_view` for non-owning views, `std::optional` for
+  "maybe", `std::variant` for alternatives.
+- `const` and `constexpr` by default; mark single-argument constructors
+  `explicit`; mark `override`/`final`; `[[nodiscard]]` on results that must
+  be used.
+- Prefer algorithms and range-for over hand-written loops; `enum class` over
+  plain `enum`; `nullptr` over `NULL` or `0`; `using` over `typedef`.
+- No C-style casts; use `static_cast` and friends. No mutable global state.
+- Headers are self-contained and contain declarations, templates and
+  `inline` definitions only.
+
+## Errors
+
+Use exceptions for exceptional failures, or `std::expected` and error codes
+where the project forbids exceptions; one choice per project. Destructors
+never throw. Catch by `const&`; never `catch (...)` without rethrowing or
+logging.
+
+## Tests
+
+GoogleTest, Catch2 or doctest; run under sanitizers (`address`, `undefined`)
+in at least one build.
+
+## Tooling
+
+`clang-format`, `clang-tidy` with the Core Guidelines checks, compiler
+warnings (`-Wall -Wextra -Wpedantic`), sanitizers.
+
+Review with `QC-CPP-001`.

.agents/skills/coding-conventions/references/csharp.md

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+# C# conventions
+
+## Standard base
+
+Microsoft's C# coding conventions and .NET Framework Design Guidelines, with
+the analyzers that ship in the SDK. Target the language version of the
+project's `LangVersion` / target framework.
+
+## Naming
+
+| Element | Convention | Example |
+| --- | --- | --- |
+| Namespace | `PascalCase`, matches folder path | `Billing.Stays` |
+| Class, struct, record, enum, delegate | `PascalCase` (nouns) | `StayReader` |
+| Interface | `I` + `PascalCase` | `IStayReader` |
+| Method, property, event, public field | `PascalCase` | `ReadStays()`, `CheckIn` |
+| Constant, `static readonly` | `PascalCase` | `MaxRetries` |
+| Enum value | `PascalCase`; `[Flags]` enums are plural | `Status.NotFound` |
+| Parameter, local variable | `camelCase` | `byteCount` |
+| Private / internal field | `_camelCase` | `_buffer` |
+| Generic type parameter | `T` or `T` + `PascalCase` | `T`, `TKey` |
+| Async method | ends in `Async` | `ReadStaysAsync()` |
+| Exception, attribute | end in `Exception` / `Attribute` | `InvalidDateException` |
+| Boolean | `Is`, `Has`, `Can` prefix | `IsActive` |
+| File | the type's name, one top-level type per file | `StayReader.cs` |
+
+- Two-letter acronyms are upper case (`IO`); longer ones are `PascalCase`
+  (`Xml`, `Http`).
+
+## Formatting
+
+- `.editorconfig` checked in; `dotnet format` applies it. 4 spaces, Allman
+  braces, braces on every control-flow body.
+- File-scoped namespaces (`namespace X;`); `using` directives outside the
+  namespace, `System` first.
+- `var` when the type is obvious from the right-hand side, explicit type
+  otherwise.
+
+## Language rules
+
+- Enable nullable reference types (`<Nullable>enable</Nullable>`) and treat
+  nullable warnings as errors; do not suppress with `!` without a comment.
+- `IDisposable` owners use `using`; implement the dispose pattern only when
+  needed.
+- `async`/`await` all the way; no `.Result` or `.Wait()`; no `async void`
+  except event handlers; pass `CancellationToken` through public async APIs.
+- Prefer properties over public fields, `readonly` and `init` for
+  immutability, `record` for value-like data, pattern matching and switch
+  expressions over long `if` chains.
+- LINQ for queries, loops for side effects; do not enumerate a sequence twice.
+- String interpolation over concatenation; `StringBuilder` in loops;
+  `DateTimeOffset` over `DateTime` for points in time; `decimal` for money.
+- XML documentation comments (`///`) on public types and members.
+
+## Errors
+
+Throw specific exceptions (`ArgumentNullException`, custom types); validate
+arguments at the public boundary (`ArgumentNullException.ThrowIfNull`). Catch
+the narrowest type; `throw;` (not `throw ex;`) to rethrow. Never an empty
+`catch`.
+
+## Tests
+
+xUnit, NUnit or MSTest; names like `Method_Condition_Expected`; one behaviour
+per test; no dependence on order, time or the network.
+
+## Tooling
+
+`dotnet format`, the .NET analyzers (`AnalysisLevel`, `EnforceCodeStyleInBuild`)
+and optionally StyleCop.Analyzers, configured in `.editorconfig`.
+
+Review with `QC-CS-001`.

.agents/skills/coding-conventions/references/python.md

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+# Python conventions
+
+## Standard base
+
+PEP 8 (style), PEP 257 (docstrings), PEP 484 and later (type hints). Target
+the Python version declared in `pyproject.toml`.
+
+## Naming
+
+| Element | Convention | Example |
+| --- | --- | --- |
+| Package / module | short `snake_case` | `billing`, `stay_reader.py` |
+| Class, exception | `PascalCase`; exceptions end in `Error` | `StayReader`, `InvalidDateError` |
+| Function, method, variable, parameter | `snake_case` | `total_price`, `read_stays()` |
+| Constant (module level) | `UPPER_SNAKE` | `MAX_RETRIES` |
+| Internal (not public API) | one leading underscore | `_parse_row` |
+| Type variable | short `PascalCase`; `_co` / `_contra` for variance | `T`, `KeyT`, `ItemT_co` |
+| Boolean | `is_`, `has_`, `can_` prefix | `is_active` |
+| Test file / function | `test_<module>.py` / `test_<behavior>_<condition>` | `test_total_when_empty` |
+
+- Avoid name mangling (`__name`) unless you need it to prevent a subclass clash.
+- Never use `l`, `O` or `I` as single-letter names.
+- Do not shadow builtins (`list`, `id`, `type`); add a trailing underscore
+  (`type_`) only as a last resort.
+
+## Formatting
+
+- 4 spaces, no tabs. Maximum line length set once in the formatter config
+  (88 with `ruff format`; 79 if the project follows PEP 8 strictly).
+- Imports at the top, grouped standard library / third party / local, one
+  blank line between groups, no wildcard imports.
+- Double quotes for strings unless the formatter says otherwise.
+- Trailing commas in multi-line literals and calls.
+
+## Language rules
+
+- Annotate every function signature (parameters and return, `-> None` too).
+  Modern syntax: `X | None`, `list[str]`. Avoid `Any` without a comment.
+- `pathlib` over `os.path`; f-strings over `%` or `.format`; `enum` over
+  magic strings; `dataclass` (frozen where possible) over ad-hoc dicts.
+- No mutable default arguments; no bare `except:`; no `print` for logging
+  (use `logging`).
+- Use context managers (`with`) for files, locks and connections.
+- Prefer comprehensions over `map`/`filter` with lambdas; keep them simple.
+- Docstrings (PEP 257) on public modules, classes and functions; say what,
+  not how.
+
+## Errors
+
+Raise specific exceptions; catch the narrowest type; re-raise with
+`raise ... from err` to keep the cause. Do not use exceptions for normal
+control flow.
+
+## Tests
+
+`pytest`; one behaviour per test; `tmp_path` for files; fakes over mocks where
+a simple fake is possible; tests do not depend on order or on the network.
+
+## Tooling
+
+`ruff` (lint and format) and `mypy --strict` (types), configured in
+`pyproject.toml`. Architecture rules (layers, ports, dataframes) are in
+`.agents/rules/python.md` and the `python-developer` agent; this sub-skill
+covers naming and style only.
+
+Review with `QC-PY-001`.

.agents/skills/coding-conventions/references/shell.md

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+# Shell conventions (bash)
+
+## Standard base
+
+Bash 4 or later, POSIX `test` semantics through `[[ ]]`. Start every script
+with `#!/usr/bin/env bash` and `set -euo pipefail`. State the bash version and
+the external tools it needs in the header comment.
+
+## Naming
+
+| Element | Convention | Example |
+| --- | --- | --- |
+| Script file | `kebab-case.sh`, executable | `check-plan.sh`, `new-artifact.sh` |
+| Function | `snake_case`, a verb | `read_registry`, `die` |
+| Local variable, parameter | `snake_case`, declared with `local` | `msgfile`, `changed` |
+| Constant, environment variable | `UPPER_SNAKE` | `PLAN_GATE`, `PROJECT_ROOT` |
+| Boolean | `is_` / `has_` prefix, value `0` or `1` | `is_enabled=1` |
+
+- Name a script and its functions by what they do, not how.
+- Do not shadow a command with a function of the same name.
+
+## Formatting
+
+- 2 spaces, no tabs. One command per line; `then` and `do` on the same line as
+  `if` and `for`. Keep lines near 80 characters; break long pipelines at `|`.
+- Format with `shfmt -i 2 -ci`; lint with `shellcheck`. Commit the project's
+  `.editorconfig` or `.shellcheckrc` with the code.
+
+## Language rules
+
+- **Quote every expansion** (`"$var"`, `"${arr[@]}"`); use arrays, not
+  space-separated strings, for lists. Use `[[ ]]`, not `[ ]`, and `$(...)`,
+  not backticks.
+- Declare function variables `local`; no globals except constants.
+- Parse options with `case` and `shift`, check required arguments with
+  `"${1:?usage: ...}"`, and print a usage line on bad input.
+- Read input with `read -r`; iterate files with globs or `find -print0`, never
+  by parsing `ls`.
+- Use `mktemp` for temporary files and remove them with `trap ... EXIT`; never
+  a fixed `/tmp` name.
+
+## Errors and exit codes
+
+- Errors go to standard error, start with `error:`, say what is wrong and what
+  to do, and end the script with a non-zero exit code (`die` helper).
+- `0` is success, `1` a failed check or bad input, `2` a usage error; document
+  any other code in the header.
+- Never swallow a failure with `|| true` without a comment that says why.
+
+## Safety
+
+- A script that changes state outside its own directory defaults to a dry run
+  or asks for an explicit flag (`--apply`, `--force`); say so in the header.
+- Never echo a token or password, put one on a command line, or commit one;
+  read secrets from the environment or a gitignored file.
+- Do not `eval` input; do not build a command from unvalidated text.
+
+## Tools
+
+Formatter `shfmt`, linter `shellcheck`, syntax check `bash -n`. These are the
+recommended tools, not a pipeline: enforcing them in CI is outside this
+framework's scope.