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/Migrations/20260303132952_InitialCreate.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable