Introduce S3-compatible storage support and update local/dev configuration.
- .claude: add "WebSearch" to local settings
- backend/.env.example: add USE_S3 flag and detailed S3/MinIO (RustFS) example env vars + comments to explain dev vs production usage
- backend/vontor_cz/settings.py: refactor to use USE_S3 boolean; set STATIC_ROOT; configure STORAGES for local filesystem vs S3 backends; add handling for S3 endpoint (MinIO/RustFS) vs real AWS S3 including path-style addressing, URL construction, and sensible AWS defaults
- docker-compose.yml: add rustfs to service dependencies, include rustfs in networks, change frontend port mapping to 8001:80, and add rustfs-data volume binding
These changes enable using a local S3-compatible backend (RustFS/MinIO) in development while keeping the option to swap to real AWS S3 for production.
