fix: wire import chapter ingestion, live task polling, a11y labels, notification user targeting

- NewBookImporter now takes *Store instead of raw *minio.Client (same package access)
- Runner Dependencies gains ChapterIngester interface; storeImportedChapters no-op removed
- store.IngestChapters is now actually called after PDF/EPUB extraction
- BookImport and ChapterIngester wired in runner main.go
- CreateImportTask interface gains initiatorUserID param; threaded through store/asynq/handler
- domain.ImportTask gains InitiatorUserID field; parseImportTask populates it
- Runner notifies initiator (falls back to 'admin' when empty)
- UI: import task list polls every 3s while any task is pending/running
- UI: label[for] + input[id] fix for a11y warnings in admin import page

backend/internal/asynqqueue/producer.go

@@ -88,8 +88,8 @@ func (p *Producer) CreateTranslationTask(ctx context.Context, slug string, chapt
 }
 
 // CreateImportTask creates a PocketBase record then enqueues an Asynq job for PDF/EPUB import.
-func (p *Producer) CreateImportTask(ctx context.Context, slug, title, fileType, objectKey string) (string, error) {
-	id, err := p.pb.CreateImportTask(ctx, slug, title, fileType, objectKey)
+func (p *Producer) CreateImportTask(ctx context.Context, slug, title, fileType, objectKey, initiatorUserID string) (string, error) {
+	id, err := p.pb.CreateImportTask(ctx, slug, title, fileType, objectKey, initiatorUserID)
 	if err != nil {
 		return "", err
 	}