style(backend): apply dotnet format whitespace normalization

- Applied dotnet format to 24 files in backend/
- Corrects spacing, indentation, and formatting consistency
- No functional changes to code logic

Ultraworked with Sisyphus <https://github.com/code-yeongyu/oh-my-opencode>
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/WorkClub.Tests.Integration/Data/MigrationTests.cs

@@ -78,10 +78,10 @@ public class MigrationTests : IAsyncLifetime
 
         // TenantId indexes
         Assert.Contains(indexes, i => i.Contains("tenant_id"));
-        
+
         // ClubId indexes
         Assert.Contains(indexes, i => i.Contains("club_id"));
-        
+
         // Status indexes for WorkItem
         Assert.Contains(indexes, i => i.Contains("status"));
     }