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.Api/Middleware/TenantValidationMiddleware.cs

@@ -19,7 +19,7 @@ public class TenantValidationMiddleware
             return;
         }
 
-        if (!context.Request.Headers.TryGetValue("X-Tenant-Id", out var tenantIdHeader) || 
+        if (!context.Request.Headers.TryGetValue("X-Tenant-Id", out var tenantIdHeader) ||
             string.IsNullOrWhiteSpace(tenantIdHeader))
         {
             context.Response.StatusCode = StatusCodes.Status400BadRequest;