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/storage.go

@@ -86,6 +86,7 @@ type StorageBackendView struct {
 	UsageBytes   int64
 	UsageLabel   string
 	InUse        bool
+	InUseReason  string
 	SpeedTests   []StorageSpeedTest
 	CanSpeedTest bool
 }
@@ -132,6 +133,14 @@ func (s *StorageService) Backend(id string) (StorageBackend, error) {
 	return s.backendFromConfig(cfg)
 }
 
+func (s *StorageService) BackendForMaintenance(id string) (StorageBackend, error) {
+	cfg, err := s.BackendConfig(id)
+	if err != nil {
+		return nil, err
+	}
+	return s.backendFromConfig(cfg)
+}
+
 func (s *StorageService) BackendConfig(id string) (StorageBackendConfig, error) {
 	id = strings.TrimSpace(id)
 	if id == "" || id == StorageBackendLocal {
@@ -340,21 +349,6 @@ func (s *StorageService) SaveBackendConfig(cfg StorageBackendConfig) error {
 	})
 }
 
-func (s *StorageService) DisableBackend(id string, inUse bool) error {
-	if id == "" || id == StorageBackendLocal {
-		return fmt.Errorf("local storage cannot be disabled")
-	}
-	if inUse {
-		return fmt.Errorf("storage backend is in use")
-	}
-	cfg, err := s.BackendConfig(id)
-	if err != nil {
-		return err
-	}
-	cfg.Enabled = false
-	return s.SaveBackendConfig(cfg)
-}
-
 func (s *StorageService) DeleteBackend(id string, inUse bool) error {
 	if id == "" || id == StorageBackendLocal {
 		return fmt.Errorf("local storage cannot be deleted")