feat(storage): add S3 backend support and advanced upload limits

- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.

backend/libs/web/renderer.go

@@ -21,6 +21,7 @@ type PageData struct {
 	ImageURL    string
 	CurrentYear int
 	CurrentUser any
+	CSRFToken   string
 	Data        any
 }