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/core/config.py

@@ -6,11 +6,19 @@ class Settings(BaseSettings):
     app_name: str = "Image Proxy Service"
     debug: bool = True
     
-    # 캐시 설정
+    # 캐시 설정 (MinIO 전환 시에도 로컬 임시 파일용)
     cache_dir: Path = Path("/app/cache")
     max_cache_size_gb: int = 10
     cache_ttl_days: int = 30
     
+    # MinIO 설정
+    use_minio: bool = True  # MinIO 사용 여부
+    minio_endpoint: str = "minio:9000"
+    minio_access_key: str = "minioadmin"
+    minio_secret_key: str = "minioadmin"
+    minio_bucket_name: str = "image-cache"
+    minio_secure: bool = False
+    
     # 이미지 설정
     max_image_size_mb: int = 20
     allowed_formats: list = ["jpg", "jpeg", "png", "gif", "webp", "svg"]