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.Infrastructure/Data/AppDbContext.cs

@@ -18,7 +18,7 @@ public class AppDbContext : DbContext
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
         base.OnModelCreating(modelBuilder);
-        
+
         modelBuilder.ApplyConfigurationsFromAssembly(typeof(AppDbContext).Assembly);
     }
 }