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/CmsAlbumBrowser.razor

@@ -189,7 +189,9 @@ else
 
         if (count == 0)
         {
-            Snackbar.Add($"'{row.Release.Title}' has no tracks to delete.", Severity.Info);
+            // Orphaned release: every track was soft-deleted earlier, leaving a 0-track row that
+            // cannot be cleared by deleting tracks. Delete the release record directly instead.
+            await ConfirmAndDeleteEmptyReleaseAsync(row);
             return;
         }
 
@@ -231,6 +233,42 @@ else
         else
         {
             Snackbar.Add($"{count - failures} of {count} track(s) deleted; {failures} failed.", Severity.Warning);
+            await OnReleasesChanged.InvokeAsync();
+        }
+        StateHasChanged();
+    }
+
+    // Delete an orphaned release (0 live tracks) via the release endpoint. Mirrors the track-cascade
+    // delete path's row lifecycle: confirm, guard with IsDeleting, then remove the row and notify the
+    // parent so the cached VM.Albums stays in sync with what is shown.
+    private async Task ConfirmAndDeleteEmptyReleaseAsync(AlbumRow row)
+    {
+        var confirmed = await DialogService.ShowMessageBox(
+            title: "Delete release",
+            markupMessage: new MarkupString(
+                $"<strong>{WebUtility.HtmlEncode(row.Release.Title)}</strong> has no tracks. Delete this empty release record?"),
+            yesText: "Delete",
+            cancelText: "Cancel");
+
+        if (confirmed != true) return;
+
+        row.IsDeleting = true;
+        StateHasChanged();
+
+        var result = await CmsTrackService.DeleteReleaseAsync(row.Release.Id);
+
+        row.IsDeleting = false;
+
+        if (result.Success)
+        {
+            Snackbar.Add($"Deleted '{row.Release.Title}'.", Severity.Success);
+            _rows.Remove(row);
+            await OnReleasesChanged.InvokeAsync();
+        }
+        else
+        {
+            var error = result.Messages.FirstOrDefault()?.Message ?? "Unknown error";
+            Snackbar.Add($"Delete failed: {error}", Severity.Error);
         }
         StateHasChanged();
     }