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/asynqqueue/consumer.go

@@ -37,6 +37,10 @@ func (c *Consumer) FinishAudioTask(ctx context.Context, id string, result domain
 	return c.pb.FinishAudioTask(ctx, id, result)
 }
 
+func (c *Consumer) FinishTranslationTask(ctx context.Context, id string, result domain.TranslationResult) error {
+	return c.pb.FinishTranslationTask(ctx, id, result)
+}
+
 func (c *Consumer) FailTask(ctx context.Context, id, errMsg string) error {
 	return c.pb.FailTask(ctx, id, errMsg)
 }
@@ -51,6 +55,10 @@ func (c *Consumer) ClaimNextAudioTask(_ context.Context, _ string) (domain.Audio
 	return domain.AudioTask{}, false, nil
 }
 
+func (c *Consumer) ClaimNextTranslationTask(_ context.Context, _ string) (domain.TranslationTask, bool, error) {
+	return domain.TranslationTask{}, false, nil
+}
+
 func (c *Consumer) HeartbeatTask(_ context.Context, _ string) error { return nil }
 
 func (c *Consumer) ReapStaleTasks(_ context.Context, _ time.Duration) (int, error) { return 0, nil }

backend/internal/asynqqueue/producer.go

@@ -73,6 +73,12 @@ func (p *Producer) CreateAudioTask(ctx context.Context, slug string, chapter int
 	return id, nil
 }
 
+// CreateTranslationTask creates a PocketBase record. Translation tasks are
+// not currently dispatched via Asynq — the runner picks them up via polling.
+func (p *Producer) CreateTranslationTask(ctx context.Context, slug string, chapter int, lang string) (string, error) {
+	return p.pb.CreateTranslationTask(ctx, slug, chapter, lang)
+}
+
 // CancelTask delegates to PocketBase; Asynq jobs may already be running and
 // cannot be reliably cancelled, so we only update the audit record.
 func (p *Producer) CancelTask(ctx context.Context, id string) error {