feat(api): add auditable map revision history - #73

Summary

Implements the map revision history requested in #12.

• Adds persistent, append-only map revision records with author, timestamp, operation, before/after snapshots, and metadata.
• Records paint, clear, publish, discard, revert, undo, redo, and rollback operations.
• Adds admin endpoints to list and inspect revisions, compute readable diffs, undo/redo the latest operation, and rollback to an arbitrary revision.
• Keeps published state intact when undoing a publish and returns requiresRepublish so the restored draft must be explicitly published.
• Adds transactional map-head tracking so a new edit clears the redo pointer.

Verification

• tsc --noEmit passes for api/.
• Express 5 route registration was smoke-tested successfully.
• git diff --check passes.
• Integration tests require PostgreSQL/Docker, which are not installed in the local environment.

Closes #12

GrantFox OpenAO bounty submission. Please review the implementation against the acceptance criteria before any reward is issued.