Align repository snapshots with GitHub Latest

[vrtmrz]

Align repository snapshot publication with GitHub's observed Latest-release behaviour while preserving prereleases for component-specific previews.

GitHub marked the first normal repository snapshot as Latest even though the workflow passed --latest=false, so the previous documented contract did not match the platform behaviour.

Summary

• allow GitHub to mark repository snapshots as the Latest normal release
• document repository snapshots as the repository-wide milestone
• require Fancy Kit Harness releases to remain prereleases
• add a workflow contract test covering the normal-release flags

Verification

• node scripts/publish-repository-snapshot-workflow.test.mjs
• actionlint .github/workflows/publish-repository-snapshot.yml
• npm run check:release-tools (37 tests)
• NODE_OPTIONS=--max-old-space-size=3072 npm run verify:workspace
• git diff --check