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)

DeepDrftAPI/Controllers/TrackController.cs

@@ -431,6 +431,22 @@ public class TrackController : ControllerBase
         return StatusCode(500, error);
     }
 
+    // DELETE api/track/release/{id} ([ApiKeyAuthorize])
+    // Soft-delete a release row directly. Used by the albums browser to remove an orphaned release
+    // (one with no live tracks). "release" is a literal segment, declared here in the literal-route
+    // block so it never resolves to the parameterized "{trackId}" GET.
+    [ApiKeyAuthorize]
+    [HttpDelete("release/{id:long}")]
+    public async Task<ActionResult> DeleteRelease(long id, CancellationToken cancellationToken)
+    {
+        var result = await _sqlTrackService.DeleteRelease(id, cancellationToken);
+        if (result.Success) return Ok();
+
+        var error = result.Messages.FirstOrDefault()?.Message ?? "unknown error";
+        _logger.LogError("DeleteRelease failed for id {Id}: {Error}", id, error);
+        return StatusCode(500, error);
+    }
+
     // --- Parameterized routes ---
 
     [HttpGet("{trackId}")]