feat(18-01): add BatchWriteProgress event constant

- Add BatchWriteProgress to tag writing events const block in events.go
- Regenerate frontend/src/events.ts via genevents codegen tool

backend/events/events.go

@@ -71,4 +71,5 @@ const (
 // Tag writing events.
 const (
 	TrackMetadataChanged = "TrackMetadataChanged"
+	BatchWriteProgress   = "BatchWriteProgress"
 )