fix(skills-hub): stop shipping a degenerate index when GitHub taps collapse (#42347)

The Skills Hub lost every api.github.com-backed source — the OpenAI,
Anthropic, HuggingFace, NVIDIA, gstack, Claude Marketplace and Well-Known
tabs all vanished — while ClawHub/skills.sh/LobeHub/browse.sh survived. A
GitHub API rate limit during the docs-deploy crawl zeroed all three
api.github.com sources (github / claude-marketplace / well-known) at once.

Two compounding bugs let the broken index reach the live site:

1. build_skills_index.py wrote the output file BEFORE the health check, so
   even when the github floor (30) tripped and the script exited 2, the
   degenerate file was already on disk. deploy-site.yml then swallowed the
   exit code with `|| echo non-fatal` and extract-skills.py read the partial
   index. Fix: run the health check first, write the file only when healthy,
   exit without writing on failure. Removed the non-fatal swallow in
   deploy-site.yml so a collapse fails the deploy and the last good site
   stays live (Pages serves the previous build).

2. The build-time GitHub listing path returned [] on a 403 rate-limit without
   retrying or flagging it, so a rate-limited crawl looked identical to an
   empty source. Fix: a shared _github_get() helper on GitHubSource with
   retry/backoff (honors Retry-After / X-RateLimit-Reset on 403/429, backs
   off on 5xx + transport errors) and flags is_rate_limited. Routed
   _list_skills_in_repo and _fetch_file_content through it; gave
   ClaudeMarketplaceSource a persistent GitHubSource + is_rate_limited so the
   builder can name the rate limit as the cause instead of '0 results'.

Added tests/scripts/test_build_skills_index_health.py pinning both contracts:
a degenerate crawl exits non-zero and writes no file; a healthy crawl writes
the index with github/claude-marketplace/well-known all present.

.github/workflows/deploy-site.yml

@@ -59,12 +59,22 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          # Always rebuild — the file isn't committed (gitignored), so a
-          # fresh checkout starts without it and we want the freshest crawl
-          # in every deploy. Failure is non-fatal: extract-skills.py will
-          # fall back to the legacy snapshot cache and the Skills Hub page
-          # still renders, just without the latest community catalog.
-          python3 scripts/build_skills_index.py || echo "Skills index build failed (non-fatal)"
+          # Rebuild the unified catalog. The file is gitignored, so a fresh
+          # checkout starts without it and we want the freshest crawl in
+          # every deploy.
+          #
+          # This MUST be fatal. build_skills_index.py runs a health check and
+          # exits non-zero WITHOUT writing the output file when a source
+          # collapses (e.g. a GitHub API rate limit zeroes the github /
+          # claude-marketplace / well-known taps all at once). Letting the
+          # deploy continue would either (a) ship a degenerate index missing
+          # whole hubs — the June 2026 regression where OpenAI/Anthropic/
+          # HuggingFace/NVIDIA tabs vanished — or (b) fall through to a
+          # local-only catalog. Failing here keeps the last good deployment
+          # live (GitHub Pages serves the previous build) instead of
+          # publishing a broken catalog. Re-run the workflow once the
+          # transient rate limit clears.
+          python3 scripts/build_skills_index.py
 
       - name: Extract skill metadata for dashboard
         run: python3 website/scripts/extract-skills.py