CRITICAL: Fixed metadata index corruption on update() operations where
removalMetadata only contained custom metadata + type, while entityForIndexing
contained ALL indexed fields. This caused 7 fields to accumulate on every
update, eventually making queries return 0 results.
- Fix removalMetadata to include all indexed fields (src/brainy.ts)
- Add validateIndexConsistency() and getIndexStats() public APIs
- Add auto-corruption detection and repair on startup
- Add getOrAssignSync() for EntityIdMapper persistence
- Add comprehensive regression tests
