Detect and fix drift between documented and actual Firestore indexes
Keep FIRESTORE_INDEXES.md and firestore.indexes.json aligned to prevent query errors.
FIRESTORE_INDEXES.mdfirestore.indexes.json.agent/artifacts/{conversation-id}/firestore_index_sync.mdrg for diffingFIRESTORE_INDEXES.mdPass/Fail: Pass only if all checks above are satisfied.