feat(website): add markdown-it-py README parser and inline renderer tests

Introduce readme_parser.py which parses README.md into structured
section data using the markdown-it-py AST. Includes TypedDicts for
ParsedEntry/ParsedSection, slugify(), render_inline_html(), and
render_inline_text(). Add test_readme_parser.py covering HTML escaping,
link rendering, emphasis, strong, and code_inline for both renderers.

Co-Authored-By: Claude <[email protected]>