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/BatchEdit.razor

@@ -7,6 +7,7 @@
 @attribute [Authorize]
 
 @inject ICmsTrackService CmsTrackService
+@inject CmsTrackBrowserViewModel VM
 @inject AuthenticationStateProvider AuthStateProvider
 @inject NavigationManager Navigation
 @inject ISnackbar Snackbar
@@ -447,6 +448,11 @@
                 StateHasChanged();
             }
 
+            // Either branch changed catalogue data, so the browse caches are stale regardless of
+            // whether every track saved. Invalidate before navigating (or staying) so the /tracks
+            // album and genre lists re-fetch.
+            VM.Invalidate();
+
             if (failed == 0)
             {
                 Snackbar.Add($"Saved {succeeded} track(s).", Severity.Success);