feat(services/insta-render): Dockerfile + requirements + env.example (SP-3 scaffold)

Windows WSL2 Docker용 Chromium 워커 컨테이너 기본 골격.
다음 task에서 main.py, worker.py, card_renderer.py 작성.

Plan-B-Insta Phase 2 시작.

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

services/insta-render/.env.example

@@ -0,0 +1,17 @@
+# Plan-B-Insta — Windows insta-render worker
+
+# NAS Redis 큐
+REDIS_URL=redis://192.168.45.54:6379
+
+# NAS internal webhook
+NAS_BASE_URL=http://192.168.45.54:18700
+INTERNAL_API_KEY=__copy_from_nas_dotenv__
+
+# NAS SMB mount 안의 미디어 디렉토리 (/mnt/nas/webpage/data/insta/)
+INSTA_MEDIA_ROOT=/mnt/nas/webpage/data/insta
+
+# nginx 서빙 prefix (NAS webhook payload에 보낼 result_path 만들 때)
+INSTA_MEDIA_URL_PREFIX=/media/insta
+
+# Jinja 템플릿 디렉토리 (이 컨테이너 안)
+CARD_TEMPLATE_DIR=/app/templates