[Paururo]

What changes

• Docs tab. Every long page now lives in the site's design: a page list, contents that follow the reading, previous and next links, a search box over all pages (press /) and an edit link to GitHub. tools/build_docs.py builds the pages from the markdown, which stays the source and still reads on GitHub.
• Code boxes follow the theme. In the light theme they are light instead of black.
• How it works. A new page follows one empty cell through seven animated drawings: the matrix says absent, the gene's sequence, the search, what the hit is, the neighbours, the policy, and what gets written down. The reader picks what the search finds (seven cases), whether the neighbours agree and the policy, and the drawings and the decision change with them. It works with reduced motion, on phones and in both themes.
• Every page has the same header, with How it works in it.

Checks

tools/check_site.py now also:

• fails if a documentation page no longer matches its markdown (fix: python3 tools/build_docs.py);
• checks links and anchors on every documentation page;
• holds the walkthrough to src/pipeline.rs: its policy table must equal matrix_policy_corrects, every state must be one evidence_state writes, every rescue_type a form RescueType prints, every matrix action one matrix_action writes, and every column one of ORTHOLOGY_EVIDENCE_COLUMNS.

Each new check was broken on purpose and failed as it should. Locally fmt, clippy, the tests, the build, check_site.py --run-tutorial and the auto-merge gate check all pass, and every page fits at 360 and 390 px with no sideways scroll.