Add freshness validation and the required docs pull-request check #162

Target

Implement this ticket in lastobelus/lastcode-docs after the first content and media set exists.

Acceptance

• Add one repository command and one GitHub check named docs / validate.
• Check the covered LastCode commit, registry hash, affected feature IDs, acknowledgements, docs evidence, and enabled capture commits.
• Check page structure, internal links, media, privacy patterns, accessibility, README references, vendored-skill hashes, frozen dependencies, focused tests, and the production build.
• Report external-link failures as warnings.
• Enforce the approved media and repository budgets.
• Require one maintainer approval, dismiss it after a push, disable auto-merge, and block Merge until docs / validate passes.
• Seed the first freshness record against the shared LastCode release commit.
• Do not generate or rewrite captures in GitHub CI.

This check protects publication. It does not promise continuous freshness, security, uptime, or concurrent-writer safety.