[C-Achard]

Adds --docs mkdocs option for MkDocs Material template. Meant for projects needing an API reference built from code directly.

[Copilot]

🟢 Approval recommended

No active review issues are recorded for the MkDocs backend addition.

No open issues 🎉

What changed in this PR

Adds --docs mkdocs to the project generator, offering MkDocs Material with a docstring-based API reference alongside the existing Jupyter Book backend.

Changes:

• Adds MkDocs dependencies, configuration, SCENE styling, and a GitHub Pages workflow.
• Extends backend checks and adds an end-to-end MkDocs build test.
• Documents backend selection and updates setup guidance and repository notes.

File	Description
TODO.md	Removes previous work items and updates repository-move notes.
tests/​test_cli.py	Checks backend-specific output, shared images, dependencies, and MkDocs builds.
src/​scene_repo_template/​skeleton/​mkdocs/​mkdocs.yml.tmpl	Configures Material, automatic API navigation, and docstring rendering.
src/​scene_repo_template/​skeleton/​mkdocs/​dot-github/​workflows/​docs.yml	Builds documentation and deploys it to GitHub Pages.
src/​scene_repo_template/​skeleton/​mkdocs/​docs/​stylesheets/​scene.css	Adds SCENE colours and footer styling.
src/​scene_repo_template/​skeleton/​mkdocs/​docs/​index.md.tmpl	Provides the generated documentation homepage.
src/​scene_repo_template/​cli.py	Registers the MkDocs backend and its dependencies and README guidance.
docs/​index.md	Corrects introductory wording.
docs/​guides/​using-the-template.md	Explains backend selection, switching, and publishing.
docs/​guides/​development-guide.md	Renames the page heading to “Collaborating on code.”

_{Review effort: Balanced}