[PerAlexandersson]

Connects the catalog site with symmetricfunctions.com (SymCat).

What changes

• Shared bibliography. scripts/symcat_sync.py snapshots the public SymCat feeds
  (site-labels.json, bibliography.json) into website/symcat/, keeping only the entries the
  pages cite. Pages declare references = [...] in their metadata and cite inline with
  [@Key] / [@Key, Thm. 2.4]. Each page gets a generated reference list with BibTeX in
  <details>.
• Statement links. sf:label links and declaration-level symcat = "label" point to SymCat
  statements; the 93 absolute SymCat URLs in docstrings are now sf: targets.
• Manifest. catalog-manifest.json lists each page's declarations, with URL and SymCat label.
  This is meant to drive subtle "formalized in Lean" badges on SymCat later.
• Hosting. build_challenge_pages.py takes --base-path and --site-origin. GitHub Pages
  stays the host for now; this prepares a later lean.symmetricfunctions.com.
• CI. Runs the new scripts/test_symcat_sync.py.

Migration

• 178 page/key assignments on 94 pages, using 123 SymCat keys. (The commit message says 170
  on 81, which is a miscount.)
• Matches use exact DOI, exact arXiv id, or a unique normalised title.
• 42 of the keys were added to SymCat's bibliography.bib for this PR.
• 37 works with no source entry stay as prose, for example Descartes, Budan, Fourier and
  unpublished manuscripts.
• Lean files change only inside module docstrings (checked mechanically for all 99 files).

Checks (local)

• Focused build of the 99 touched modules passes.
• lake exe lint-style and check_proof_status pass.
• build_challenge_pages.py --check passes (106 pages), as does audit_challenge_catalog.py --check.
• test_challenge_catalog.py (29 tests) and test_symcat_sync.py pass.

The snapshot was taken from a local SymCat build. The 42 new bibliography keys go live on
symmetricfunctions.com with its next deploy.

🤖 Generated with Claude Code