feat(account): /account/update_region_code (accept-only)

SVSim.UnitTests/Controllers/AccountControllerUpdateRegionCodeTests.cs

@@ -0,0 +1,24 @@
+using System.Net;
+using System.Text;
+using NUnit.Framework;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Controllers;
+
+public class AccountControllerUpdateRegionCodeTests
+{
+    [TestCase(0)]
+    [TestCase(1)]
+    public async Task UpdateRegionCode_accepts(int initializeFlag)
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync(tutorialState: 0);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var requestJson = $$"""{"initialize_flag":{{initializeFlag}},"viewer_id":"0","steam_id":0,"steam_session_ticket":""}""";
+        var response = await client.PostAsync("/account/update_region_code",
+            new StringContent(requestJson, Encoding.UTF8, "application/json"));
+
+        Assert.That(response.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+    }
+}