Add repository snapshot release workflow

[vrtmrz]

Add a manually dispatched repository snapshot release workflow that publishes reviewed main commits under date-based tags.

Summary

• add publish-repository-snapshot.yml for normal, non-latest GitHub Releases;
• require a real YYYY.MM.DD.N version, the exact main commit SHA, and an exact confirmation;
• keep workspace packages and Fancy Kit Harness independently versioned; and
• document the workflow and cover its release-selection validator with focused tests.

Verification

• actionlint .github/workflows/publish-repository-snapshot.yml
• npm run check:release-tools — 36 tests passed
• NODE_OPTIONS=--max-old-space-size=3072 npm run verify:workspace