Add AuthScopedFilter to set AddedWho via middleware

Introduce AuthScopedFilter to automatically set the AddedWho property on IAuthScoped commands using configuration, and register it globally for all controllers. Remove manual AddedWho assignment from ResultViewController. Make AddedWho nullable in AuthScope and IAuthScoped.

src/ReC.API/Program.cs

@@ -54,7 +54,10 @@ try
         });
     });
 
-    builder.Services.AddControllers();
+    builder.Services.AddControllers(options =>
+    {
+        options.Filters.Add<AuthScopedFilter>();
+    });
     // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
     builder.Services.AddEndpointsApiExplorer();
     builder.Services.AddSwaggerGen(c =>