feat(storage): support deleting backends and improve admin UI

- Implement storage backend deletion, which automatically resets default storage settings and user-specific overrides when a backend is removed.
- Add unit tests covering the delete action and its cleanup side effects.
- Improve admin UI responsiveness, fixing table scrolling, flex wrapping, and text truncation for long storage backend names.
- Update security documentation to clarify trusted proxy configurations and explain how trusted proxies are protected from automatic bans.

backend/libs/services/settings.go

@@ -233,6 +233,29 @@ func (s *SettingsService) UpdateUploadPolicy(settings UploadPolicySettings) erro
 	})
 }
 
+func (s *SettingsService) ResetStorageBackend(backendID string) (bool, bool, error) {
+	backendID = strings.TrimSpace(backendID)
+	if backendID == "" || backendID == StorageBackendLocal {
+		return false, false, nil
+	}
+	settings, err := s.UploadPolicy()
+	if err != nil {
+		return false, false, err
+	}
+	resetAnonymous := settings.AnonymousStorageBackend == backendID
+	resetUser := settings.UserStorageBackend == backendID
+	if !resetAnonymous && !resetUser {
+		return false, false, nil
+	}
+	if resetAnonymous {
+		settings.AnonymousStorageBackend = StorageBackendLocal
+	}
+	if resetUser {
+		settings.UserStorageBackend = StorageBackendLocal
+	}
+	return resetAnonymous, resetUser, s.UpdateUploadPolicy(settings)
+}
+
 func (s *SettingsService) Usage(subjectType, subject string, now time.Time) (UsageRecord, error) {
 	key := usageKey(subjectType, subject, now)
 	var record UsageRecord