MIL-010 task 7: guide, README, wiki pages in three languages

Task: MIL-010#7
Refs #161

docs/wiki/Home.md

@@ -13,12 +13,12 @@ A collection of reusable Gitea Actions workflows for DevOps professionals and so
 
 This repository is the central collection of reusable automation for TirSystem repositories. The primary repository lives at `git.tirsystem.com` (Gitea) and is push-mirrored to GitHub.
 
-It contains nine workflows: metadata sync to the GitHub mirror, wiki publishing (called by each repository), shared quality checks for Python and shell, for C and C++ and for C#, a release workflow, the publishing of accepted milestones and the repository's own validation. They are listed with their purpose and a diagram under [Workflows](#workflows).
+It contains ten workflows: metadata sync to the GitHub mirror, wiki publishing (called by each repository), shared quality checks for Python and shell, for C and C++ and for C#, code metrics and coverage badges, a release workflow, the publishing of accepted milestones and the repository's own validation. They are listed with their purpose and a diagram under [Workflows](#workflows).
 
 
 ## Workflows
 
-Nine workflows live in this repository. A **scoped** workflow is delivered by the instance to every repository of the TirSystem organizations and needs nothing in the repository; a **reusable** workflow is called by a repository with `uses:`; the others run only here. The diagrams are PlantUML source.
+Ten workflows live in this repository. A **scoped** workflow is delivered by the instance to every repository of the TirSystem organizations and needs nothing in the repository; a **reusable** workflow is called by a repository with `uses:`; the others run only here. The diagrams are PlantUML source.
 
 | Workflow | File | Kind | Starts on | Purpose |
 | --- | --- | --- | --- | --- |
@@ -27,6 +27,7 @@ Nine workflows live in this repository. A **scoped** workflow is delivered by th
 | Quality checks | [`quality-checks.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/quality-checks.yml) | Reusable (`workflow_call`) | a call from another repository | Runs ruff, mypy, shellcheck and shfmt on the tracked files and changes nothing |
 | Quality checks C++ | [`quality-checks-cpp.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/quality-checks-cpp.yml) | Reusable (`workflow_call`) | a call from another repository | Runs clang-format and clang-tidy at exact versions on the tracked C and C++ files and changes nothing |
 | Quality checks C# | [`quality-checks-csharp.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/quality-checks-csharp.yml) | Reusable (`workflow_call`) | a call from another repository | Runs `dotnet format` and `dotnet build` on an exact .NET SDK 10 or later and changes nothing |
+| Code metrics | [`code-metrics.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/code-metrics.yml) | Reusable (`workflow_call`) | a call from another repository | Counts the code files and the lines of code (without comment and blank lines), reads a Cobertura coverage report and commits three SVG badges to a `badges` branch |
 | Publish own wiki | [`publish-own-wiki.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/publish-own-wiki.yml) | This repository only | push to `main` that changes `docs/wiki/**`, manual | Calls the reusable Publish wiki pages workflow for the wiki of this repository |
 | Release | [`release.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/release.yml) | This repository only | manual | Creates the version tag, the release page and the major tag after the checks |
 | Publish accepted milestones | [`sync-milestones.yml`](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/.gitea/workflows/sync-milestones.yml) | This repository only | push to `main` that changes `docs/milestones/**` or `docs/sqa/reviews/**`, manual (dry run by default) | Creates or updates the Gitea milestone and issues of every milestone that is Accepted with a Go review |
@@ -234,6 +235,50 @@ deactivate Workflow
 @enduml
 ```
 
+### Code metrics
+
+A reusable workflow that counts the code files and the lines of code (without comment and blank lines) of a repository and publishes them, with the test coverage, as three SVG badges on a `badges` branch, called with `uses: TirSystem/github-action/.gitea/workflows/code-metrics.yml@v1` (ADR-0010). It needs `contents: write` and runs no test: an earlier job of the caller produces a Cobertura XML coverage report and uploads it as an artifact ([guide](CodeMetrics)).
+
+#### Workflow
+
+```plantuml
+@startuml
+title Code metrics and coverage badges (reusable workflow)
+
+autonumber
+
+actor "Calling repository\nuses: ...code-metrics.yml@v1" as Caller
+participant "Gitea Actions\ncode-metrics" as Workflow
+participant "Branch badges\nof the caller" as Branch
+
+Caller -> Workflow: workflow_call with working-directory, exclude,\ncoverage-report and thresholds
+activate Workflow
+
+Workflow -> Workflow: Check out the caller and the shared scripts
+Workflow -> Workflow: Validate the inputs
+alt an input is invalid
+  Workflow --> Caller: Fail with [configuration]
+end
+
+Workflow -> Workflow: Download the coverage artifact (when given)
+Workflow -> Workflow: Count code files and lines of code
+alt a coverage report is given but missing or malformed
+  Workflow --> Caller: Fail with [configuration] that names the file
+else
+  Workflow -> Workflow: Write code-files.svg, code-lines.svg\nand coverage.svg
+end
+
+Workflow -> Branch: Compare with the files of the branch
+alt no badge changed
+  Workflow --> Caller: Notice: nothing to commit, pass
+else
+  Workflow -> Branch: One commit with [skip ci]
+  Workflow --> Caller: Badges published
+end
+deactivate Workflow
+@enduml
+```
+
 ### Release
 
 Started by hand by a maintainer; with `dry_run` `true` (the default) it only checks (see the [release process](https://git.tirsystem.com/TirSystem/github-action/src/branch/main/guides/release-process.md)).