refactor(insta-lab): remove Playwright + slim Dockerfile (SP-4)

NAS에서 더 이상 카드 렌더 안 함 → Windows insta-render 워커로 완전 이전.
- card_renderer.py를 1줄 deprecation stub로 교체
- main.py의 import card_renderer 제거 + startup/shutdown hook 정리
- requirements.txt에서 playwright 삭제
- Dockerfile에서 Chromium 30+ dep 라인 + playwright install 제거 → image ~50% 감소
- test_card_renderer.py 폐기 (Windows 측 test_worker.py가 대체)
- test_main.py의 create_slate 테스트를 Redis-push 플로우에 맞게 업데이트

Plan-B-Insta Phase 3 완료.

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

insta-lab/app/main.py

@@ -18,7 +18,7 @@ from .config import (
 )
 import redis.asyncio as aioredis
 
-from . import db, news_collector, keyword_extractor, card_writer, card_renderer, trend_collector
+from . import db, news_collector, keyword_extractor, card_writer, trend_collector
 from .internal_router import router as internal_router
 
 logger = logging.getLogger(__name__)
@@ -42,13 +42,11 @@ app.add_middleware(
 async def on_startup():
     os.makedirs(INSTA_DATA_PATH, exist_ok=True)
     db.init_db()
-    # Chromium browser pool 초기화 (CHECK_POINT 중기-6)
-    await card_renderer.init_browser()
 
 
 @app.on_event("shutdown")
 async def on_shutdown():
-    await card_renderer.shutdown_browser()
+    pass
 
 
 @app.get("/health")