Dispose existing CancellationTokenSource before creating new one

Prevents potential resource leaks if InitializeAllVMCoreComponentsAsync is called multiple times.

Co-authored-by: YBTopaz8 <41630728+YBTopaz8@users.noreply.github.com>

Author: Copilot

Dimmer/Dimmer/ViewModel/BaseViewModel.cs

@@ -680,7 +680,11 @@ await lastFMRealm.WriteAsync(() =>
             $"{DateTime.Now}: Finished InitializeAllVMCoreComponentsAsync in {duration.TotalSeconds} seconds.");
 
         // Initialize background caching with proper error handling and cancellation support
+        // Dispose existing token if it exists (e.g., if this method is called multiple times)
+        _backgroundCachingCts?.Cancel();
+        _backgroundCachingCts?.Dispose();
         _backgroundCachingCts = new CancellationTokenSource();
+        
         _ = Task.Run(async () =>
         {
             try