[walkccc]

Closes #564

#564's screenshot is GitHub's preview, where $$ inside a list item doesn't render. This PR makes the repo render on GitHub too and builds/deploys in CI. Best reviewed commit by commit.

Commits

1. main.yaml, requirements.txt, AGENTS.md: CI runs mkdocs build --strict on every PR and uploads the built site as an artifact; pushes to main deploy to gh-pages (same peaceiris setup as walkccc/LeetCode). Versions pinned (mkdocs==1.6.1, mkdocs-material==9.7.7) because MkDocs 2.0 drops theme overrides. AGENTS.md (+ CLAUDE.md) documents layout, math conventions, and how to verify.
2. 15-1.md, 16.4.md: two source bugs: an empty $$ in 16.4 ("call it $$." → "$D$") and a $$…$$ in the middle of a sentence in 15-1.
3. *.md, mkdocs.yml, katex.js: the 86 $$ blocks nested in list items become ```math fences (plain LaTeX inside). superfences turns them into \[…\] for KaTeX on the site; GitHub renders them natively.
4. main.yaml, check_math.py, AGENTS.md: CI lint that rejects $$ in list items and \\\\ inside ```math.

Verification

• Site: extracted every expression KaTeX receives from the built site before and after. All 15,855 match exactly in content, order, and display/inline mode.
• GitHub: rendered the 22 changed files through GitHub's Markdown API before and after: display blocks 71 → 171, and the inline "losses" are display equations GitHub used to squash inline.
• Escaping stays as before (\\\\, \\{). GitHub applies the same Markdown escaping inside $…$, so switching to plain LaTeX would break GitHub's rendering instead.
• Tried Prettier as a formatter and dropped it: it rewrites ^* to ^_ inside inline math on 12+ pages.

After merge, the first push to main deploys via Actions, so check the Actions tab and the site.

🤖 Generated with Claude Code