docs: add searchable Sourcey skill catalog

[tzwkb]

Summary

• add a Sourcey 3.6.5 static catalog for 24 governed Runx skills
• pin extraction and provenance to upstream commit 5afc25a83edf1c1320df7ac0d78c36f1523b5677
• include generated search, navigation, Open Graph images, and llms.txt context exports
• verify page coverage, immutable source links, local links and fragments, search/navigation coverage, and credential markers
• include a source-derived maintainer gap report

This complements the existing curated operator docs; it does not replace them.

Closes #340

Validation

• clean full clone: pnpm test:fast (16 files, 176/176 tests)
• node --test docs/sourcey-catalog/*.test.mjs (37/37)
• node docs/sourcey-catalog/extract.mjs (24 pages from the pinned commit)
• node docs/sourcey-catalog/build.mjs (Sourcey 3.6.5, 24 pages)
• node docs/sourcey-catalog/verify.mjs (ok: true, 24/24 Markdown, HTML, navigation, search, and immutable source links)
• zero broken local links and zero credential findings
• governed run: Runx CLI 0.7.1 executed the official Sourcey 0.1.1 graph with Sourcey 3.6.5; all 11 steps succeeded
• root receipt: runx:receipt:sha256:1c6b2a31d2f743173169523fbff419bebc5da33d415224419aea1cffa1ba5f85
• receipt verification: production Ed25519 mode, 12-receipt tree, valid=true, zero findings
• independent review: approved with no remaining Critical, Important, or Minor findings

[tzwkb]

@auscaster, could you review whether this project-owned Sourcey catalog fits the repository docs direction? The PR is mergeable, has no attached CI, and includes reproducible build/extract/verify tests plus a verified Runx receipt. I can reduce the generated output or adjust the integration path if preferred.