feat(music-lab): verify_internal_key + /api/internal/music/update (SP-6)

X-Internal-Key 헤더 검증 dependency (insta-lab 동일 패턴).
Windows music-render webhook 수신 endpoint — update_task + 옵션 add_track.
Plan-B-Music Phase 1 (수신부).

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

music-lab/app/internal_router.py

@@ -0,0 +1,61 @@
+"""SP-6 — Windows music-render → NAS internal webhook.
+
+POST /api/internal/music/update
+- X-Internal-Key 인증 필수
+- music_tasks 테이블 row update (status, progress, message, audio_url, error)
+- 옵션 `track` 페이로드가 있으면 music_library에 add_track 호출
+"""
+from __future__ import annotations
+
+import logging
+from typing import Any, Dict, Optional
+
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel, Field
+
+from . import db
+from .auth import verify_internal_key
+
+logger = logging.getLogger(__name__)
+router = APIRouter()
+
+
+class UpdatePayload(BaseModel):
+    task_id: str
+    status: str = Field(..., description="processing|succeeded|failed")
+    progress: int = Field(..., ge=0, le=100)
+    message: str = ""
+    audio_url: Optional[str] = None
+    error: Optional[str] = None
+    track: Optional[Dict[str, Any]] = None
+
+
+@router.post(
+    "/api/internal/music/update",
+    dependencies=[Depends(verify_internal_key)],
+)
+def music_update(payload: UpdatePayload):
+    task = db.get_task(payload.task_id)
+    if task is None:
+        raise HTTPException(404, f"task not found: {payload.task_id}")
+
+    db.update_task(
+        payload.task_id,
+        payload.status,
+        payload.progress,
+        message=payload.message,
+        audio_url=payload.audio_url,
+        error=payload.error,
+    )
+
+    if payload.track:
+        try:
+            db.add_track(payload.track)
+        except Exception:
+            logger.exception("add_track 실패 task=%s (무시)", payload.task_id)
+
+    logger.info(
+        "internal/music/update task=%s status=%s progress=%d",
+        payload.task_id, payload.status, payload.progress,
+    )
+    return {"ok": True}