4a0c17c318
- Replace object lock with SemaphoreSlim(1,1) on both DirectoryIndexDirectory and VaultIndexDirectory; SaveIndexAsync now executes inside the semaphore so mutate+persist is atomic - ReloadIndexAsync acquires the semaphore before LoadIndexAsync so disk load and in-memory swap are atomic with respect to concurrent writes - HasIndexEntry and GetEntryMetadata converted to async Task with WaitAsync; MediaVault.GetEntryAsync call sites updated accordingly - TrackRepository.Update throws InvalidOperationException when Id not found instead of silently calling Create; service layer catches and wraps as fail result