fix: refresh stale browse cache on track edits and allow deleting empty releases

- Add CmsTrackBrowserViewModel.Invalidate(); called from TrackEdit/BatchEdit on save or delete so album/genre cache is invalidated and re-fetches on next mode switch
- CmsAlbumBrowser now handles 0-track releases: confirm dialog + DeleteReleaseAsync instead of early return; partial-failure path also fires OnReleasesChanged to trigger cache invalidation
- TrackList.OnAlbumsChanged now calls VM.Invalidate() so genres stay fresh after any album delete
- UnifiedTrackService.DeleteAsync cascades release soft-delete when last live track is removed (non-fatal; logs on failure)
- New DELETE api/track/release/{id} endpoint (ApiKeyAuthorize) for direct release soft-delete
- EF migration SoftDeleteOrphanedReleases backfills existing orphaned release rows via raw SQL (data-only, no schema change)

DeepDrftManager/Components/Pages/Tracks/TrackList.razor

@@ -69,9 +69,13 @@
 @code {
     private CmsTrackGrid? _grid;
 
-    // The album browser owns its own row state and removes a deleted release locally. We only need to
-    // re-render the page chrome; VM.Albums is intentionally not re-fetched (cached for the circuit).
-    private void OnAlbumsChanged() => StateHasChanged();
+    // The album browser owns its own row state and removes a deleted release locally. Invalidate the
+    // VM cache so genres and album counts reflect the deletion on next mode switch.
+    private void OnAlbumsChanged()
+    {
+        VM.Invalidate();
+        StateHasChanged();
+    }
 
     // Local state for the parent-owned "Generate All Missing" bulk run.
     private bool _bulkRunning;