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/upload.go

@@ -553,6 +553,28 @@ func (s *UploadService) DeleteBox(boxID string) error {
 	return s.DeleteBoxWithSource(boxID, "admin")
 }
 
+func (s *UploadService) DeleteBoxesForStorageBackend(backendID, source string) (int, error) {
+	backendID = normalizeBackendID(backendID)
+	if backendID == StorageBackendLocal {
+		return 0, fmt.Errorf("local storage cannot be deleted")
+	}
+	boxes, err := s.ListBoxes(0)
+	if err != nil {
+		return 0, err
+	}
+	deleted := 0
+	for _, box := range boxes {
+		if s.BoxStorageBackendID(box) != backendID {
+			continue
+		}
+		if err := s.DeleteBoxWithSource(box.ID, source); err != nil {
+			return deleted, err
+		}
+		deleted++
+	}
+	return deleted, nil
+}
+
 func (s *UploadService) DeleteBoxWithToken(boxID, token string) error {
 	box, err := s.GetBox(boxID)
 	if err != nil {
@@ -572,7 +594,12 @@ func (s *UploadService) DeleteBoxWithSource(boxID, source string) error {
 		return err
 	}
 	if box.ID != "" {
-		if backend, err := s.storage.Backend(s.BoxStorageBackendID(box)); err == nil {
+		backendID := s.BoxStorageBackendID(box)
+		backend, err := s.storage.Backend(backendID)
+		if err != nil {
+			backend, err = s.storage.BackendForMaintenance(backendID)
+		}
+		if err == nil {
 			if err := backend.DeletePrefix(context.Background(), box.ID); err != nil {
 				return err
 			}