feat(insta-lab): wire internal_router + Redis client (SP-4 prep)

main.py에 internal_router include + 모듈 레벨 redis client.
requirements.txt에 redis>=5.0 추가 (playwright 제거는 Task 12에서).

Plan-B-Insta Phase 1 마무리. Task 11에서 _bg_render를 Redis push로 전환.

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

insta-lab/requirements.txt

@@ -8,3 +8,4 @@ playwright==1.48.0
 Pillow>=10
 pytest>=8.0
 pytest-asyncio>=0.24
+redis>=5.0