add custom website build system

Replaces MkDocs with a bespoke Python site generator using Jinja2 templates
and Markdown. Adds uv for dependency management, GitHub Actions workflow for
deployment, and Makefile targets for local development (fetch_stars, build,
preview, deploy).

Co-Authored-By: Claude <noreply@anthropic.com>

Makefile

@@ -1,14 +1,14 @@
 site_install:
-	pip install -r requirements.txt
+	uv sync --no-dev
 
-site_link:
-	ln -sf $(CURDIR)/README.md $(CURDIR)/docs/index.md
+fetch_stars:
+	uv run python website/fetch_github_stars.py
 
-site_preview: site_link
-	mkdocs serve
+site_build:
+	uv run python website/build.py
 
-site_build: site_link
-	mkdocs build
+site_preview: site_build
+	python -m http.server -d website/output/ 8000
 
-site_deploy: site_link
-	mkdocs gh-deploy --clean
+site_deploy: site_build
+	@echo "Deploy via GitHub Actions (push to master)"