fix(1978): register lipsync_gpu task in worker celery imports

Worker celery_app.conf.imports was missing app.tasks.lipsync_gpu,
so lipsync_gpu_process_async.apply_async() messages were sent to
broker but never consumed by any worker, leaving lipsync_jobs stuck
at status=processing forever.

apps/worker/worker_app/celery_app.py

@@ -48,6 +48,9 @@ celery_app.conf.imports = (
     # PYTHONPATH=/app/apps/api 下，app.tasks.lipsync_tts 可直接导入且不触发 apps/api/__init__.py
     # （apps/api/__init__.py 会 from .main import app，级联加载整个 FastAPI 栈，Worker 中不需要且会导致注册失败）
     "app.tasks.lipsync_tts",
+    # #1998 GPU MuseTalk 异步推理：wait_for_result→签名 URL→回写 lipsync_jobs
+    # 必须在 Worker 侧注册，否则 apply_async 消息无人消费，job 永远卡在 processing
+    "app.tasks.lipsync_gpu",
 )
 
 # Celery Beat 定时任务调度