Add Pretty Table project: plan, accepted documents and code

Business Case, Stakeholder Analysis, Project Plan and milestone MIL-001
with review records RC-001 to RC-003, then the Python project: PrettyTable
Pokemon table, constants, pytest tests, pyproject.toml, Doxyfile, CI
workflow and README.

Task: MIL-001#1
Task: MIL-001#2
Task: MIL-001#3
Task: MIL-001#4
Task: MIL-001#5
Task: MIL-001#6
Task: MIL-001#7
Task: MIL-001#8

.agents/skills/artifact/references/ADR.md

@@ -0,0 +1,25 @@
+# Architecture Decision Record (ADR)
+
+Files: `docs/adr/adr-NNNN-kebab-case-title.md`. `NNNN` is 4-digit and
+sequential; the ID is `ADR-NNNN` and must match the filename number (an
+intentional exception to the usual 3-digit IDs). Use
+`new-artifact.sh ADR --file docs/adr/adr-NNNN-title.md`.
+
+Cite in `CrossReference` the artifacts this decision is about (pass each
+with `--cite <ID>=<path>`); ADR has no fixed candidate list.
+
+## Required sections (after Metadata / Version History)
+
+- **Context** — the problem, the options evaluated and the forces
+  (cost, risk, constraints).
+- **Decision** — the outcome in one or two sentences, no hedging.
+- **Consequences** — two bold labels, **Positive:** and **Negative:**, each
+  with a bullet list.
+- **Affected Artifacts** — other artifacts impacted, as `[ID]` links, or a
+  single `-` if none.
+
+Allowed statuses: `Proposed`, `Accepted`, `Rejected`, `Deprecated`,
+`Superseded by ADR-NNNN`; no others (an ADR is never `Approved`). Status
+changes (`Proposed` → `Accepted` → `Deprecated` / `Superseded by ADR-NNNN`, or
+`Proposed` → `Rejected`) are new rows in `## Version History` (only the two
+latest are kept; earlier ones stay in git); never rewrite a retained row.