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/requirements.txt

@@ -0,0 +1,10 @@
+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+requests==2.32.3
+redis>=5.0
+httpx>=0.27
+openai>=1.50.0
+google-cloud-storage>=2.18.0
+pytest>=8.0
+pytest-asyncio>=0.24
+respx>=0.21