- Add BatchFailure and BatchResult types for structured batch outcomes
- Add cancelBatch channel and suppressEvents flag to TagWriter struct
- Add CancelBatchWrite method for mid-batch cancellation from frontend
- Add BatchWriteTrackTags method processing tracks sequentially
- Emit BatchWriteProgress event per-track with current/total/succeeded/failed
- Suppress per-track TrackMetadataChanged; emit single event after batch
- Wails bindings auto-generated for BatchWriteTrackTags and CancelBatchWrite
- tagwriter namespace with BatchResult/BatchFailure in models.ts