refactor(music-lab): batch_generator _generate_one_track → Redis push (SP-6)

기존 직접 run_suno_generation 호출 + asyncio.to_thread를
Redis push (queue:music-render, job_type=suno_generation) +
task 상태 polling 패턴으로 변경. 결과는 task_id로 music_library 조회.
Plan-B-Music Phase 3 (cutover 3/4).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

music-lab/app/batch_generator.py

@@ -102,8 +102,10 @@ async def run_batch(batch_id: int) -> None:
 
 async def _generate_one_track(*, title: str, genre: str, duration_sec: int,
                               params: dict) -> int | None:
-    """기존 Suno generate 호출 + 완료까지 polling. 성공 시 새 track id, 실패 시 None."""
-    from .suno_provider import run_suno_generation
+    """Redis 큐에 push + task 상태 polling. 성공 시 새 track id, 실패 시 None."""
+    import json
+    from datetime import datetime, timezone, timedelta
+    from .main import redis_client  # 같은 컨테이너 — 동일 redis 클라이언트 공유
 
     task_id = str(uuid.uuid4())
     suno_params = {
@@ -116,11 +118,23 @@ async def _generate_one_track(*, title: str, genre: str, duration_sec: int,
         "key": params["key"],
         "scale": params["scale"],
         "prompt": params.get("prompt_modifier", ""),
+        "provider": "suno",
+        "model": "V4",
+        "instrumental": False,
+        "lyrics": "",
     }
     db.create_task(task_id, suno_params, provider="suno")
 
-    # Suno background task — 우리가 await로 기다림 (BackgroundTasks 미사용)
-    asyncio.create_task(asyncio.to_thread(run_suno_generation, task_id, suno_params))
+    # Redis push (Windows music-render가 BLPOP 처리)
+    kst = timezone(timedelta(hours=9))
+    payload = {
+        "task_id": task_id,
+        "kind": "music",
+        "job_type": "suno_generation",
+        "params": suno_params,
+        "submitted_at": datetime.now(kst).isoformat(),
+    }
+    await redis_client.rpush("queue:music-render", json.dumps(payload))
 
     waited = 0
     while waited < TRACK_GEN_TIMEOUT_S:
@@ -131,14 +145,7 @@ async def _generate_one_track(*, title: str, genre: str, duration_sec: int,
             continue
         status = task.get("status")
         if status == "succeeded":
-            # task["track"] 또는 task["result"]["track"] 형태 시도, 없으면 task_id로 조회
-            tr = task.get("track")
-            if tr and isinstance(tr, dict):
-                return tr.get("id")
-            result = task.get("result", {}) or {}
-            if isinstance(result, dict) and isinstance(result.get("track"), dict):
-                return result["track"].get("id")
-            # Fallback: music_library에서 task_id로 검색
+            # Windows webhook이 add_track 했으므로 task_id로 검색
             track = db.get_track_by_task_id(task_id)
             if track:
                 return track.get("id")