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/requirements.txt

@@ -8,4 +8,5 @@ python-multipart==0.0.6
 pydantic==2.5.3
 pydantic-settings==2.1.0
 motor==3.3.2
-redis==5.0.1
+redis==5.0.1
+minio==7.2.3