feat: add image fetch with proxy support and registry proxy config

Backend:
- Add image fetch handler using go-containerregistry
- Support HTTP/HTTPS and SOCKS5 proxy protocols
- Pull images from remote registries (Docker Hub, etc.)
- Store fetched images as blobs and manifests
- Add timeout handling (60s for descriptor fetch)
- Add detailed logging for pull progress
- Add /api/v1/registry/image/fetch endpoint

Frontend:
- Add registry proxy configuration field
- Add "获取镜像" button and dialog
- Add proxy checkbox and input in fetch dialog
- Add LinearProgress feedback during fetch
- Add multi-stage Snackbar notifications
- Auto-refresh image list after successful fetch
- Fix download filename regex (remove trailing quote)
- Adjust button colors for better UI consistency

Dependencies:
- Add github.com/google/go-containerregistry for OCI operations
- Add golang.org/x/net/proxy for SOCKS5 support

🤖 Generated with [Qoder](https://qoder.com)

internal/api/api.go

@@ -47,6 +47,7 @@ func Init(ctx context.Context, address string, db *gorm.DB, store store.Store) (
 		registryAPI.Get("/image/list", registry.RegistryImageList(ctx, db, store))
 		registryAPI.Get("/image/download/*", registry.RegistryImageDownload(ctx, db, store))
 		registryAPI.Post("/image/upload", registry.RegistryImageUpload(ctx, db, store))
+		registryAPI.Post("/image/fetch", registry.RegistryImageFetch(ctx, db, store))
 		// registry config apis
 		registryAPI.Get("/config", registry.RegistryConfigGet(ctx, db, store))
 		registryAPI.Post("/config", registry.RegistryConfigSet(ctx, db, store))