feat(audio): WAV streaming, bulk audio generation admin endpoints, cancel/resume

- Add StreamAudioWAV() to pocket-tts and Kokoro clients; pocket-tts streams
  raw WAV directly (no ffmpeg), Kokoro requests response_format:wav with stream:true
- GET /api/audio-stream supports ?format=wav for lower-latency first-byte delivery;
  WAV cached separately in MinIO as {slug}/{n}/{voice}.wav
- Add GET /api/admin/audio/jobs with optional ?slug filter
- Add POST /api/admin/audio/bulk {slug, voice, from, to, skip_existing, force}
  where skip_existing=true (default) resumes interrupted bulk jobs
- Add POST /api/admin/audio/cancel-bulk {slug} to cancel all pending/running tasks
- Add CancelAudioTasksBySlug to taskqueue.Producer + asynqqueue implementation
- Add AudioObjectKeyExt to bookstore.AudioStore for format-aware MinIO keys

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/storage/minio.go

@@ -109,10 +109,17 @@ func ChapterObjectKey(slug string, n int) string {
 	return fmt.Sprintf("%s/chapter-%06d.md", slug, n)
 }
 
-// AudioObjectKey returns the MinIO object key for a cached audio file.
+// AudioObjectKeyExt returns the MinIO object key for a cached audio file
+// with a custom extension (e.g. "mp3" or "wav").
+// Format: {slug}/{n}/{voice}.{ext}
+func AudioObjectKeyExt(slug string, n int, voice, ext string) string {
+	return fmt.Sprintf("%s/%d/%s.%s", slug, n, voice, ext)
+}
+
+// AudioObjectKey returns the MinIO object key for a cached MP3 audio file.
 // Format: {slug}/{n}/{voice}.mp3
 func AudioObjectKey(slug string, n int, voice string) string {
-	return fmt.Sprintf("%s/%d/%s.mp3", slug, n, voice)
+	return AudioObjectKeyExt(slug, n, voice, "mp3")
 }
 
 // AvatarObjectKey returns the MinIO object key for a user avatar image.

backend/internal/storage/store.go

@@ -376,6 +376,10 @@ func (s *Store) AudioObjectKey(slug string, n int, voice string) string {
 	return AudioObjectKey(slug, n, voice)
 }
 
+func (s *Store) AudioObjectKeyExt(slug string, n int, voice, ext string) string {
+	return AudioObjectKeyExt(slug, n, voice, ext)
+}
+
 func (s *Store) AudioExists(ctx context.Context, key string) bool {
 	return s.mc.objectExists(ctx, s.mc.bucketAudio, key)
 }
@@ -574,6 +578,28 @@ func (s *Store) CancelTask(ctx context.Context, id string) error {
 		map[string]string{"status": string(domain.TaskStatusCancelled)})
 }
 
+func (s *Store) CancelAudioTasksBySlug(ctx context.Context, slug string) (int, error) {
+	filter := fmt.Sprintf(`slug='%s'&&(status='pending'||status='running')`, slug)
+	items, err := s.pb.listAll(ctx, "audio_jobs", filter, "")
+	if err != nil {
+		return 0, fmt.Errorf("CancelAudioTasksBySlug list: %w", err)
+	}
+	cancelled := 0
+	for _, raw := range items {
+		var rec struct {
+			ID string `json:"id"`
+		}
+		if json.Unmarshal(raw, &rec) == nil && rec.ID != "" {
+			if patchErr := s.pb.patch(ctx,
+				fmt.Sprintf("/api/collections/audio_jobs/records/%s", rec.ID),
+				map[string]string{"status": string(domain.TaskStatusCancelled)}); patchErr == nil {
+				cancelled++
+			}
+		}
+	}
+	return cancelled, nil
+}
+
 // ── taskqueue.Consumer ────────────────────────────────────────────────────────
 
 func (s *Store) ClaimNextScrapeTask(ctx context.Context, workerID string) (domain.ScrapeTask, bool, error) {