Use sorted username dropdown for character owner editing

RpgRoller.Tests/Api/AuthApiTests.cs

@@ -29,4 +29,22 @@ public sealed class AuthApiTests : ApiTestBase
         var invalidLogin = await client.PostAsJsonAsync("/api/auth/login", new LoginRequest("alice", "wrong-password"));
         Assert.Equal(HttpStatusCode.BadRequest, invalidLogin.StatusCode);
     }
-}
+
+    [Fact]
+    public async Task UsernamesEndpoint_RequiresAuthAndReturnsAlphabeticalList()
+    {
+        using var factory = CreateFactory();
+        using var client = factory.CreateClient(new() { AllowAutoRedirect = false });
+
+        await RegisterAsync(client, "zoe", "Password123", "Zoe");
+        await RegisterAsync(client, "amy", "Password123", "Amy");
+        await RegisterAsync(client, "bob", "Password123", "Bob");
+
+        var unauthorized = await client.GetAsync("/api/users/usernames");
+        Assert.Equal(HttpStatusCode.Unauthorized, unauthorized.StatusCode);
+
+        await LoginAsync(client, "bob", "Password123");
+        var usernames = await GetAsync<IReadOnlyList<string>>(client, "/api/users/usernames");
+        Assert.Equal(["amy", "bob", "zoe"], usernames);
+    }
+}

RpgRoller.Tests/Services/ServiceAuthTests.cs

@@ -56,4 +56,22 @@ public sealed class ServiceAuthTests
         Assert.True(login.Succeeded);
         Assert.Equal(2, hasher.HashCalls);
     }
-}
+
+    [Fact]
+    public void GetUsernames_RequiresAuthAndReturnsSortedUsernames()
+    {
+        using var harness = ServiceTestSupport.CreateHarness();
+        var service = harness.Service;
+
+        service.Register("zoe", "Password123", "Zoe");
+        service.Register("amy", "Password123", "Amy");
+        service.Register("bob", "Password123", "Bob");
+
+        var unauthorized = service.GetUsernames(string.Empty);
+        Assert.False(unauthorized.Succeeded);
+
+        var session = ServiceTestSupport.GetValue(service.Login("bob", "Password123")).SessionToken;
+        var usernames = ServiceTestSupport.GetValue(service.GetUsernames(session));
+        Assert.Equal(["amy", "bob", "zoe"], usernames);
+    }
+}