refactor(music-lab): sync helpers → Windows HTTP forward + cleanup (SP-6)

/api/music/{lyrics, credits, timestamped-lyrics, style-boost}
모두 sync_forward 모듈로 위임 → Windows :18711/api/music-render/sync/*.
SUNO_API_KEY가 NAS에 없으므로 직접 호출 불가.
run_*, generate_*, get_* import 제거 (Windows로 이전됨).
SUNO_MODELS만 잔존 (정적 데이터).

추가 cleanup (T11 reviewer 지적):
- _push_render_job의 datetime import를 모듈 상위로
- 11 endpoint의 unused BackgroundTasks 매개변수 제거

generate_batch: SUNO_API_KEY 체크를 os.getenv()로 전환 + 테스트 monkeypatch 갱신.

Plan-B-Music Phase 3 (cutover 2/4).

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

music-lab/app/sync_forward.py

@@ -0,0 +1,76 @@
+"""SP-6 sync helpers forward — NAS → Windows music-render.
+
+NAS music-lab의 /api/music/lyrics, /api/music/credits,
+/api/music/timestamped-lyrics, /api/music/style-boost 호출을
+Windows music-render의 /api/music-render/sync/* 로 forward.
+
+SUNO_API_KEY는 NAS에 없으므로 NAS에서 직접 호출 불가.
+"""
+from __future__ import annotations
+
+import logging
+import os
+from typing import Optional
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+MUSIC_RENDER_URL = os.getenv("MUSIC_RENDER_URL", "http://192.168.45.59:18711")
+_TIMEOUT = 60.0  # 가사 생성은 폴링 포함 ~45초
+
+
+def forward_lyrics(prompt: str) -> Optional[dict]:
+    try:
+        r = httpx.post(
+            f"{MUSIC_RENDER_URL}/api/music-render/sync/lyrics",
+            json={"prompt": prompt},
+            timeout=_TIMEOUT,
+        )
+        if r.status_code == 200:
+            return r.json()
+        logger.warning("forward_lyrics returned %d", r.status_code)
+    except Exception:
+        logger.exception("forward_lyrics 실패")
+    return None
+
+
+def forward_credits() -> Optional[dict]:
+    try:
+        r = httpx.get(
+            f"{MUSIC_RENDER_URL}/api/music-render/sync/credits",
+            timeout=30.0,
+        )
+        if r.status_code == 200:
+            return r.json()
+    except Exception:
+        logger.exception("forward_credits 실패")
+    return None
+
+
+def forward_timestamped_lyrics(task_id: str, suno_id: str) -> Optional[dict]:
+    try:
+        r = httpx.get(
+            f"{MUSIC_RENDER_URL}/api/music-render/sync/timestamped-lyrics",
+            params={"task_id": task_id, "suno_id": suno_id},
+            timeout=30.0,
+        )
+        if r.status_code == 200:
+            return r.json()
+    except Exception:
+        logger.exception("forward_timestamped_lyrics 실패")
+    return None
+
+
+def forward_style_boost(content: str) -> Optional[dict]:
+    try:
+        r = httpx.post(
+            f"{MUSIC_RENDER_URL}/api/music-render/sync/style-boost",
+            json={"content": content},
+            timeout=30.0,
+        )
+        if r.status_code == 200:
+            return r.json()
+    except Exception:
+        logger.exception("forward_style_boost 실패")
+    return None