fix: Tier2 backup status now detects drives removed from storage (not just disconnected)

Previously, removing a storage drive from the controller only marked it as
disconnected if the StoragePath entry still existed with Disconnected:true.
Drives removed entirely from storage_paths were invisible to the check,
causing Tier2 backup UI to show green "Sikeres" and scheduler to attempt
backups to a no-longer-managed destination.

New IsStoragePathKnown() method covers both cases. UI shows yellow
"Cél meghajtó leválasztva" and scheduler skips silently.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/web/handlers.go

@@ -938,6 +938,13 @@ func (s *Server) buildAppBackupRows(
 				}
 			}
 
+			// Also treat as disconnected if dest was removed from storage entirely
+			if cfg.DestinationPath != "" && !row.Tier2DestDisconnected {
+				if !s.settings.IsStoragePathKnown(cfg.DestinationPath) {
+					row.Tier2DestDisconnected = true
+				}
+			}
+
 			if row.Tier2DestDisconnected {
 				// Disconnected destination — treat as paused, not failed
 				row.Status = "yellow"