Added the ProperDocs Documentation Website

[lecode-official]

Added a documentation website, built with ProperDocs (properdocs.yml, requirements.txt) on top of the existing hand-written docs/ tree, so docs_dir needs no separate source folder. The site gets a generated "API Reference" section built at deploy time from the framework's XML documentation comments, via a new gen-files hook (docs/build/generate-api-docs.py) that shells out to the xmldoc2md local tool (newly pinned in .config/dotnet-tools.json). Because Roslyn never expands <inheritdoc/> in the emitted XML documentation file, clinet-core now also references SauceControl.InheritDoc (PrivateAssets="all") to rewrite it into real text as a build step, so the generated API docs are not full of empty members. Three more build hooks handle the smaller pieces: copying the favicon to the site root, rewriting links that point outside docs_dir into absolute GitHub URLs, and injecting the "API Reference" nav entry into the overview page. A new light/dark logo and favicon set was added under docs/assets/, along with CSS that teaches the site's Material theme to honor GitHub's #gh-dark-mode-only / #gh-light-mode-only image suffixes and to swap the header logo with the color scheme. A new "Docs" GitHub Actions workflow (.github/workflows/docs.yml) builds and deploys the site to GitHub Pages on every push to main.

Restructured the documentation to make room for this. Merged docs/developer-manual/architecture/ into a single docs/developer-manual/architecture.md, renamed contributing.md to contribution-guide.md and tooling/formatting-dprint.md to tooling/code-formatting-dprint.md, and moved design/DESIGN.md to docs/developer-manual/logo-design.md, adding a small new design/README.md that just lists the asset files left behind. Added a new "Documentation Website" article describing all of the above, and updated CLAUDE.md and the various indexes to match.

The website's own build output goes into build/documentation-website/ (site_dir in properdocs.yml), which meant a top-level build/ directory now existed in the repository for the first time. While touching that, the C# projects' bin//obj/ output was redirected into it too, so all build output — the website's and the .NET projects' alike — lives in the same place: a new Directory.Build.props under source/ (shared by clinet-core and sample-app, keyed off each project's own folder name) and another under tests/unit-tests do the redirecting. .gitignore, the shared VS Code settings, and the CSpell ignore list were all updated from the old bin//obj/ patterns to build/, and .gitignore also picks up node_modules/, .venv/, and __pycache__/ for the new NPM and Python tooling the website needed. Added shared VS Code launch.json and tasks.json files with a "Debug Sample App" launch configuration and its matching build task.

The website's Python dependencies needed pinning in a new requirements.txt to match this project's policy of never using version ranges (see Dependency Management), and since that pinning had to be introduced anyway, the linters got the same treatment on the NPM side: a new package.json / package-lock.json pins dprint, cspell, and markdownlint-cli2 instead of installing global, unlocked versions in CI and in the pre-commit hooks in .claude/settings.json — both now run npm ci once and invoke the linters through npx.

Finally, added a CLAUDE.md golden rule that changes are never staged or committed automatically — only the user does that, by hand — matching a new "Never Stage or Commit Automatically" section in the commit-messages article.

This work was done with the help of Claude Code, which built the ProperDocs site and its build hooks, wrote the GitHub Pages workflow, redirected the build output, migrated the linters to npm, and updated the documentation to match.

Closes issue #25.