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/CmsTrackService.cs

@@ -152,6 +152,39 @@ public class CmsTrackService : ICmsTrackService
         }
     }
 
+    public async Task<Result> DeleteReleaseAsync(long releaseId, CancellationToken ct = default)
+    {
+        var client = _httpClientFactory.CreateClient(ContentCmsClientName);
+
+        HttpResponseMessage response;
+        try
+        {
+            response = await client.DeleteAsync($"api/track/release/{releaseId}", ct);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Content API call failed for delete of release {ReleaseId}", releaseId);
+            return Result.CreateFailResult("Content API is unreachable.");
+        }
+
+        using (response)
+        {
+            if (response.IsSuccessStatusCode)
+            {
+                return Result.CreatePassResult();
+            }
+
+            if (response.StatusCode == HttpStatusCode.NotFound)
+            {
+                return Result.CreateFailResult("Release not found.");
+            }
+
+            var body = await response.Content.ReadAsStringAsync(ct);
+            _logger.LogError("Content API delete failed for release {ReleaseId}: {Status} {Body}", releaseId, (int)response.StatusCode, body);
+            return Result.CreateFailResult("Failed to delete release.");
+        }
+    }
+
     public async Task<ResultContainer<PagedResult<TrackDto>>> GetPagedAsync(
         int page, int pageSize, string? sortColumn, bool sortDescending,
         string? album = null, string? genre = null,