feat(video-lab): /api/internal/video/update endpoint + tests (SP-8)

UpdatePayload schema (task_id/status/progress/message/video_url/error).
404 if task not found. insta/music-lab과 동일 패턴 + video_url 필드.
Plan-B-Video Phase 1.

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

video-lab/app/internal_router.py

@@ -0,0 +1,52 @@
+"""SP-8 — Windows video-render → NAS video-lab internal webhook.
+
+POST /api/internal/video/update
+- X-Internal-Key 인증 필수
+- video_tasks row update (status, progress, message, video_url, error)
+"""
+from __future__ import annotations
+
+import logging
+from typing import 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 = ""
+    video_url: Optional[str] = None
+    error: Optional[str] = None
+
+
+@router.post(
+    "/api/internal/video/update",
+    dependencies=[Depends(verify_internal_key)],
+)
+def video_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,
+        video_url=payload.video_url,
+        error=payload.error,
+    )
+    logger.info(
+        "internal/video/update task=%s status=%s progress=%d",
+        payload.task_id, payload.status, payload.progress,
+    )
+    return {"ok": True}