feat: integrate MinIO storage for image caching service

- Replace file system storage with MinIO object storage
- Add MinIO cache implementation with 3-level directory structure
- Support dynamic switching between MinIO and filesystem via config
- Fix metadata encoding issue for non-ASCII URLs
- Successfully tested with various image sources including Korean URLs

All image service features working:
- Image proxy and download
- 5 size variants (thumb, card, list, detail, hero)
- WebP format conversion
- Cache hit/miss detection
- Background size generation

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

services/images/backend/app/api/endpoints.py

@@ -5,9 +5,14 @@ import mimetypes
 from pathlib import Path
 import hashlib
 
-from ..core.cache import cache
 from ..core.config import settings
 
+# MinIO 사용 여부에 따라 적절한 캐시 모듈 선택
+if settings.use_minio:
+    from ..core.minio_cache import cache
+else:
+    from ..core.cache import cache
+
 router = APIRouter()
 
 @router.get("/image")
@@ -113,7 +118,7 @@ async def get_stats():
     """캐시 통계 정보"""
     cache_size = await cache.get_cache_size()
     
-    # 디렉토리 구조 통계 추가
+    # 디렉토리 구조 통계 추가 (MinIO 또는 파일시스템)
     dir_stats = await cache.get_directory_stats()
     
     return {