Add comprehensive backend test suite and helper access

GameList.Tests/Support/TestClientExtensions.cs

@@ -43,4 +43,11 @@ internal static class TestClientExtensions
         var json = await response.Content.ReadFromJsonAsync<JsonElement>();
         return json.GetProperty("id").GetInt32();
     }
+
+    public static async Task<Guid> GetProfileIdAsync(this HttpClient client)
+    {
+        var me = await client.GetFromJsonAsync<JsonElement>("/api/me");
+        return Guid.Parse(me.GetProperty("id").GetString()!);
+    }
+
 }

GameList.Tests/Support/TestWebApplicationFactory.cs

@@ -79,6 +79,13 @@ internal class TestWebApplicationFactory : WebApplicationFactory<Program>
         return action(db);
     }
 
+    public Task<T> WithDbContextAsync<T>(Func<AppDbContext, Task<T>> action)
+    {
+        using var scope = Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+        return action(db);
+    }
+
     public HttpClient CreateClientWithCookies()
     {
         return CreateClient(new WebApplicationFactoryClientOptions