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/TrackEdit.razor

@@ -4,6 +4,7 @@
 @using Microsoft.AspNetCore.Components.Forms
 @attribute [Authorize]
 @inject ICmsTrackService CmsTrackService
+@inject CmsTrackBrowserViewModel VM
 @inject IHttpClientFactory HttpClientFactory
 @inject ISnackbar Snackbar
 @inject IDialogService DialogService
@@ -227,6 +228,9 @@
                 _form.TrackNumber);
             if (updated.Success)
             {
+                // Album/genre browse lists derive from this track's metadata; drop their cache so
+                // the /tracks browser re-fetches fresh data on next mode switch.
+                VM.Invalidate();
                 Snackbar.Add("Track updated.", Severity.Success);
                 await LoadAsync();
             }
@@ -276,6 +280,9 @@
             var result = await CmsTrackService.DeleteTrackAsync(Id);
             if (result.Success)
             {
+                // Deleting a track can empty or alter a release; drop the browse cache so the
+                // /tracks album and genre lists re-fetch fresh counts on next mode switch.
+                VM.Invalidate();
                 Snackbar.Add("Track deleted.", Severity.Success);
                 Nav.NavigateTo("/tracks");
             }