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/Infrastructure/IntegrationTestBase.cs

@@ -18,10 +18,10 @@ public abstract class IntegrationTestBase : IClassFixture<CustomWebApplicationFa
         var clubsJson = JsonSerializer.Serialize(clubs);
         Client.DefaultRequestHeaders.Remove("X-Test-Clubs");
         Client.DefaultRequestHeaders.Add("X-Test-Clubs", clubsJson);
-        
+
         Client.DefaultRequestHeaders.Remove("X-Test-Email");
         Client.DefaultRequestHeaders.Add("X-Test-Email", email);
-        
+
         if (!string.IsNullOrEmpty(userId))
         {
             Client.DefaultRequestHeaders.Remove("X-Test-UserId");