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)

DeepDrftData/TrackManager.cs

@@ -282,4 +282,30 @@ public class TrackManager
 
     // Delete(long) → Result is inherited from Manager<> and satisfies ITrackService.Delete
     // by signature. No override.
+
+    public async Task<Result> DeleteRelease(long id, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            await Repository.SoftDeleteReleaseAsync(id, cancellationToken);
+            return Result.CreatePassResult();
+        }
+        catch (Exception e)
+        {
+            return Result.CreateFailResult(e.Message);
+        }
+    }
+
+    public async Task<ResultContainer<int>> CountLiveTracksByRelease(long releaseId, CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var count = await Repository.CountLiveTracksByReleaseAsync(releaseId, cancellationToken);
+            return ResultContainer<int>.CreatePassResult(count);
+        }
+        catch (Exception e)
+        {
+            return ResultContainer<int>.CreateFailResult(e.Message);
+        }
+    }
 }