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/Services/ICmsTrackService.cs

@@ -40,6 +40,12 @@ public interface ICmsTrackService
     /// </summary>
     Task<Result> DeleteTrackAsync(long id, CancellationToken ct = default);
 
+    /// <summary>
+    /// Soft-delete a release record via DELETE api/track/release/{id}. Use when a release
+    /// has no live tracks and needs to be removed from the albums browser.
+    /// </summary>
+    Task<Result> DeleteReleaseAsync(long releaseId, CancellationToken ct = default);
+
     /// <summary>
     /// Fetch a page of track metadata from the Content API's <c>GET api/track/page</c>. Optional
     /// <paramref name="album"/> and <paramref name="genre"/> filters narrow the result to a single