feat(video-render): scaffold + nas_client webhook adapter (SP-7)

Dockerfile (python:3.12-slim), requirements (openai + google-cloud-storage + httpx + redis).
.env.example: OPENAI/GOOGLE/PIAPI/SEEDANCE keys + VIDEO_MEDIA_ROOT.
nas_client.webhook_update_task: call-time os.getenv (테스트 격리), respx mock 5 tests.
Plan-B-Video Phase 2.

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

services/video-render/nas_client.py

@@ -0,0 +1,54 @@
+"""NAS webhook 어댑터 — Windows worker가 NAS DB 직접 접근 못하므로 HTTP로 위임.
+
+Plan-B-Music nas_client와 동일 패턴 (call-time os.getenv으로 테스트 격리).
+"""
+from __future__ import annotations
+
+import logging
+import os
+from typing import Any, Dict, Optional
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+_TIMEOUT = 10.0
+
+
+def _post(payload: Dict[str, Any]) -> None:
+    nas_base_url = os.getenv("NAS_BASE_URL", "http://192.168.45.54:18801")
+    internal_api_key = os.getenv("INTERNAL_API_KEY", "")
+    url = f"{nas_base_url}/api/internal/video/update"
+    try:
+        r = httpx.post(
+            url,
+            headers={"X-Internal-Key": internal_api_key},
+            json=payload,
+            timeout=_TIMEOUT,
+        )
+        if r.status_code != 200:
+            logger.error("webhook %s returned %d: %s",
+                         payload.get("task_id"), r.status_code, r.text[:200])
+    except Exception:
+        logger.exception("webhook %s 호출 실패", payload.get("task_id"))
+
+
+def webhook_update_task(
+    task_id: str,
+    status: str,
+    progress: int,
+    message: str = "",
+    video_url: Optional[str] = None,
+    error: Optional[str] = None,
+) -> None:
+    payload: Dict[str, Any] = {
+        "task_id": task_id,
+        "status": status,
+        "progress": progress,
+        "message": message,
+    }
+    if video_url is not None:
+        payload["video_url"] = video_url
+    if error is not None:
+        payload["error"] = error
+    _post(payload)