feat(music-render): Dockerfile + requirements + env.example (SP-5)

Windows WSL2 Docker 컨테이너 스캐폴드.
Plan-B-Insta보다 가벼움 — Chromium 미포함, requests + httpx + redis + mutagen만.
.env.example에 SUNO_API_KEY 자리 (NAS에서 옮겨올 값).
Plan-B-Music Phase 2.

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

services/music-render/requirements.txt

@@ -0,0 +1,9 @@
+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+requests==2.32.3
+redis>=5.0
+httpx>=0.27
+mutagen==1.47.0
+pytest>=8.0
+pytest-asyncio>=0.24
+respx>=0.21