feat(translation): machine translation pipeline + admin bulk enqueue UI

- LibreTranslate client (chunks on blank lines, ≤4500 chars, 3-goroutine semaphore)
- Runner translation task loop (OTel, heartbeat, MinIO storage)
- PocketBase translation_jobs collection support (create/claim/finish/list)
- Per-chapter language switcher on chapter reader (EN/RU/ID/PT/FR, polls until done)
- Admin /admin/translation page: bulk enqueue form + live-polling jobs table
- New backend routes: POST /api/translation/{slug}/{n}, GET /api/translation/status,
  GET /api/translation/{slug}/{n}, GET /api/admin/translation/jobs,
  POST /api/admin/translation/bulk
- ListTranslationTasks added to taskqueue.Reader interface + store impl
- All builds and tests pass; svelte-check: 0 errors

backend/internal/storage/minio.go

@@ -17,12 +17,13 @@ import (
 
 // minioClient wraps the official minio-go client with bucket names.
 type minioClient struct {
-	client         *minio.Client // internal — all read/write operations
-	pubClient      *minio.Client // presign-only — initialised against the public endpoint
-	bucketChapters string
-	bucketAudio    string
-	bucketAvatars  string
-	bucketBrowse   string
+	client             *minio.Client // internal — all read/write operations
+	pubClient          *minio.Client // presign-only — initialised against the public endpoint
+	bucketChapters     string
+	bucketAudio        string
+	bucketAvatars      string
+	bucketBrowse       string
+	bucketTranslations string
 }
 
 func newMinioClient(cfg config.MinIO) (*minioClient, error) {
@@ -74,18 +75,19 @@ func newMinioClient(cfg config.MinIO) (*minioClient, error) {
 	}
 
 	return &minioClient{
-		client:         internal,
-		pubClient:      pub,
-		bucketChapters: cfg.BucketChapters,
-		bucketAudio:    cfg.BucketAudio,
-		bucketAvatars:  cfg.BucketAvatars,
-		bucketBrowse:   cfg.BucketBrowse,
+		client:             internal,
+		pubClient:          pub,
+		bucketChapters:     cfg.BucketChapters,
+		bucketAudio:        cfg.BucketAudio,
+		bucketAvatars:      cfg.BucketAvatars,
+		bucketBrowse:       cfg.BucketBrowse,
+		bucketTranslations: cfg.BucketTranslations,
 	}, nil
 }
 
 // ensureBuckets creates all required buckets if they don't already exist.
 func (m *minioClient) ensureBuckets(ctx context.Context) error {
-	for _, bucket := range []string{m.bucketChapters, m.bucketAudio, m.bucketAvatars, m.bucketBrowse} {
+	for _, bucket := range []string{m.bucketChapters, m.bucketAudio, m.bucketAvatars, m.bucketBrowse, m.bucketTranslations} {
 		exists, err := m.client.BucketExists(ctx, bucket)
 		if err != nil {
 			return fmt.Errorf("minio: check bucket %q: %w", bucket, err)
@@ -125,6 +127,12 @@ func CoverObjectKey(slug string) string {
 	return fmt.Sprintf("covers/%s.jpg", slug)
 }
 
+// TranslationObjectKey returns the MinIO object key for a translated chapter.
+// Format: {lang}/{slug}/{n:06d}.md
+func TranslationObjectKey(lang, slug string, n int) string {
+	return fmt.Sprintf("%s/%s/%06d.md", lang, slug, n)
+}
+
 // chapterNumberFromKey extracts the chapter number from a MinIO object key.
 // e.g. "my-book/chapter-000042.md" → 42
 func chapterNumberFromKey(key string) int {

backend/internal/storage/store.go

@@ -51,6 +51,7 @@ var _ bookstore.AudioStore = (*Store)(nil)
 var _ bookstore.PresignStore = (*Store)(nil)
 var _ bookstore.ProgressStore = (*Store)(nil)
 var _ bookstore.CoverStore = (*Store)(nil)
+var _ bookstore.TranslationStore = (*Store)(nil)
 var _ taskqueue.Producer = (*Store)(nil)
 var _ taskqueue.Consumer = (*Store)(nil)
 var _ taskqueue.Reader = (*Store)(nil)
@@ -535,13 +536,36 @@ func (s *Store) CreateAudioTask(ctx context.Context, slug string, chapter int, v
 	return rec.ID, nil
 }
 
+func (s *Store) CreateTranslationTask(ctx context.Context, slug string, chapter int, lang string) (string, error) {
+	cacheKey := fmt.Sprintf("%s/%d/%s", slug, chapter, lang)
+	payload := map[string]any{
+		"cache_key": cacheKey,
+		"slug":      slug,
+		"chapter":   chapter,
+		"lang":      lang,
+		"status":    string(domain.TaskStatusPending),
+		"started":   time.Now().UTC().Format(time.RFC3339),
+	}
+	var rec struct {
+		ID string `json:"id"`
+	}
+	if err := s.pb.post(ctx, "/api/collections/translation_jobs/records", payload, &rec); err != nil {
+		return "", err
+	}
+	return rec.ID, nil
+}
+
 func (s *Store) CancelTask(ctx context.Context, id string) error {
-	// Try scraping_tasks first, then audio_jobs.
+	// Try scraping_tasks first, then audio_jobs, then translation_jobs.
 	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/scraping_tasks/records/%s", id),
 		map[string]string{"status": string(domain.TaskStatusCancelled)}); err == nil {
 		return nil
 	}
-	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id),
+	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id),
+		map[string]string{"status": string(domain.TaskStatusCancelled)}); err == nil {
+		return nil
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/translation_jobs/records/%s", id),
 		map[string]string{"status": string(domain.TaskStatusCancelled)})
 }
 
@@ -571,6 +595,18 @@ func (s *Store) ClaimNextAudioTask(ctx context.Context, workerID string) (domain
 	return task, err == nil, err
 }
 
+func (s *Store) ClaimNextTranslationTask(ctx context.Context, workerID string) (domain.TranslationTask, bool, error) {
+	raw, err := s.pb.claimRecord(ctx, "translation_jobs", workerID, nil)
+	if err != nil {
+		return domain.TranslationTask{}, false, err
+	}
+	if raw == nil {
+		return domain.TranslationTask{}, false, nil
+	}
+	task, err := parseTranslationTask(raw)
+	return task, err == nil, err
+}
+
 func (s *Store) FinishScrapeTask(ctx context.Context, id string, result domain.ScrapeResult) error {
 	status := string(domain.TaskStatusDone)
 	if result.ErrorMessage != "" {
@@ -599,6 +635,18 @@ func (s *Store) FinishAudioTask(ctx context.Context, id string, result domain.Au
 	})
 }
 
+func (s *Store) FinishTranslationTask(ctx context.Context, id string, result domain.TranslationResult) error {
+	status := string(domain.TaskStatusDone)
+	if result.ErrorMessage != "" {
+		status = string(domain.TaskStatusFailed)
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/translation_jobs/records/%s", id), map[string]any{
+		"status":        status,
+		"error_message": result.ErrorMessage,
+		"finished":      time.Now().UTC().Format(time.RFC3339),
+	})
+}
+
 func (s *Store) FailTask(ctx context.Context, id, errMsg string) error {
 	payload := map[string]any{
 		"status":        string(domain.TaskStatusFailed),
@@ -608,11 +656,14 @@ func (s *Store) FailTask(ctx context.Context, id, errMsg string) error {
 	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/scraping_tasks/records/%s", id), payload); err == nil {
 		return nil
 	}
-	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id), payload)
+	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id), payload); err == nil {
+		return nil
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/translation_jobs/records/%s", id), payload)
 }
 
 // HeartbeatTask updates the heartbeat_at field on a running task.
-// Tries scraping_tasks first, then audio_jobs (same pattern as FailTask).
+// Tries scraping_tasks first, then audio_jobs, then translation_jobs.
 func (s *Store) HeartbeatTask(ctx context.Context, id string) error {
 	payload := map[string]any{
 		"heartbeat_at": time.Now().UTC().Format(time.RFC3339),
@@ -620,7 +671,10 @@ func (s *Store) HeartbeatTask(ctx context.Context, id string) error {
 	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/scraping_tasks/records/%s", id), payload); err == nil {
 		return nil
 	}
-	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id), payload)
+	if err := s.pb.patch(ctx, fmt.Sprintf("/api/collections/audio_jobs/records/%s", id), payload); err == nil {
+		return nil
+	}
+	return s.pb.patch(ctx, fmt.Sprintf("/api/collections/translation_jobs/records/%s", id), payload)
 }
 
 // ReapStaleTasks finds all running tasks whose heartbeat_at is either missing
@@ -638,7 +692,7 @@ func (s *Store) ReapStaleTasks(ctx context.Context, staleAfter time.Duration) (i
 	}
 
 	total := 0
-	for _, collection := range []string{"scraping_tasks", "audio_jobs"} {
+	for _, collection := range []string{"scraping_tasks", "audio_jobs", "translation_jobs"} {
 		items, err := s.pb.listAll(ctx, collection, filter, "")
 		if err != nil {
 			return total, fmt.Errorf("ReapStaleTasks list %s: %w", collection, err)
@@ -715,6 +769,31 @@ func (s *Store) GetAudioTask(ctx context.Context, cacheKey string) (domain.Audio
 	return t, err == nil, err
 }
 
+func (s *Store) ListTranslationTasks(ctx context.Context) ([]domain.TranslationTask, error) {
+	items, err := s.pb.listAll(ctx, "translation_jobs", "", "-started")
+	if err != nil {
+		return nil, err
+	}
+	tasks := make([]domain.TranslationTask, 0, len(items))
+	for _, raw := range items {
+		t, err := parseTranslationTask(raw)
+		if err == nil {
+			tasks = append(tasks, t)
+		}
+	}
+	return tasks, nil
+}
+
+func (s *Store) GetTranslationTask(ctx context.Context, cacheKey string) (domain.TranslationTask, bool, error) {
+	filter := fmt.Sprintf(`cache_key='%s'`, cacheKey)
+	items, err := s.pb.listAll(ctx, "translation_jobs", filter, "-started")
+	if err != nil || len(items) == 0 {
+		return domain.TranslationTask{}, false, err
+	}
+	t, err := parseTranslationTask(items[0])
+	return t, err == nil, err
+}
+
 // ── Parsers ───────────────────────────────────────────────────────────────────
 
 func parseScrapeTask(raw json.RawMessage) (domain.ScrapeTask, error) {
@@ -789,6 +868,38 @@ func parseAudioTask(raw json.RawMessage) (domain.AudioTask, error) {
 	}, nil
 }
 
+func parseTranslationTask(raw json.RawMessage) (domain.TranslationTask, error) {
+	var rec struct {
+		ID           string `json:"id"`
+		CacheKey     string `json:"cache_key"`
+		Slug         string `json:"slug"`
+		Chapter      int    `json:"chapter"`
+		Lang         string `json:"lang"`
+		WorkerID     string `json:"worker_id"`
+		Status       string `json:"status"`
+		ErrorMessage string `json:"error_message"`
+		Started      string `json:"started"`
+		Finished     string `json:"finished"`
+	}
+	if err := json.Unmarshal(raw, &rec); err != nil {
+		return domain.TranslationTask{}, err
+	}
+	started, _ := time.Parse(time.RFC3339, rec.Started)
+	finished, _ := time.Parse(time.RFC3339, rec.Finished)
+	return domain.TranslationTask{
+		ID:           rec.ID,
+		CacheKey:     rec.CacheKey,
+		Slug:         rec.Slug,
+		Chapter:      rec.Chapter,
+		Lang:         rec.Lang,
+		WorkerID:     rec.WorkerID,
+		Status:       domain.TaskStatus(rec.Status),
+		ErrorMessage: rec.ErrorMessage,
+		Started:      started,
+		Finished:     finished,
+	}, nil
+}
+
 // ── CoverStore ─────────────────────────────────────────────────────────────────
 
 func (s *Store) PutCover(ctx context.Context, slug string, data []byte, contentType string) error {
@@ -818,3 +929,25 @@ func (s *Store) GetCover(ctx context.Context, slug string) ([]byte, string, bool
 func (s *Store) CoverExists(ctx context.Context, slug string) bool {
 	return s.mc.coverExists(ctx, CoverObjectKey(slug))
 }
+
+// ── TranslationStore ───────────────────────────────────────────────────────────
+
+func (s *Store) TranslationObjectKey(lang, slug string, n int) string {
+	return TranslationObjectKey(lang, slug, n)
+}
+
+func (s *Store) TranslationExists(ctx context.Context, key string) bool {
+	return s.mc.objectExists(ctx, s.mc.bucketTranslations, key)
+}
+
+func (s *Store) PutTranslation(ctx context.Context, key string, data []byte) error {
+	return s.mc.putObject(ctx, s.mc.bucketTranslations, key, "text/markdown; charset=utf-8", data)
+}
+
+func (s *Store) GetTranslation(ctx context.Context, key string) (string, error) {
+	data, err := s.mc.getObject(ctx, s.mc.bucketTranslations, key)
+	if err != nil {
+		return "", fmt.Errorf("GetTranslation: %w", err)
+	}
+	return string(data), nil
+}