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/Repositories/TrackRepository.cs

@@ -182,6 +182,23 @@ public class TrackRepository : Repository<DeepDrftContext, TrackEntity>
         await _context.SaveChangesAsync(ct);
     }
 
+    // Soft-delete a release row in a single set-based UPDATE (no load round-trip). The !IsDeleted
+    // guard makes a repeat call a no-op rather than re-stamping updated_at on an already-deleted row.
+    public async Task SoftDeleteReleaseAsync(long id, CancellationToken ct = default)
+    {
+        await _context.Set<ReleaseEntity>()
+            .Where(r => r.Id == id && !r.IsDeleted)
+            .ExecuteUpdateAsync(s => s
+                .SetProperty(r => r.IsDeleted, true)
+                .SetProperty(r => r.UpdatedAt, DateTime.UtcNow), ct);
+    }
+
+    // Count of non-deleted tracks on a single release. Backs the delete-cascade decision in
+    // UnifiedTrackService: a release with zero live tracks after a delete is soft-deleted too.
+    // Uses Query (soft-delete filtered) so just-deleted tracks are excluded from the count.
+    public async Task<int> CountLiveTracksByReleaseAsync(long releaseId, CancellationToken ct = default)
+        => await Query.CountAsync(t => t.ReleaseId == releaseId, ct);
+
     protected override void UpdateEntity(TrackEntity target, TrackEntity source)
     {
         base.UpdateEntity(target, source); // copies CreatedAt, UpdatedAt, IsDeleted