Lobby: include HostUserId in GameStateDto and let client derive host status; update tests

SlipItIn.Server.Tests/GameServiceTests.cs

@@ -40,6 +40,18 @@ public class GameServiceTests
         await Assert.ThrowsAsync<InvalidOperationException>(() => _sut.CreateGameAsync(999));
     }
 
+    [Fact]
+    public async Task GetGameStateAsync_IncludesHostUserId()
+    {
+        using var db = _factory.CreateDbContext();
+        var host = TestDbHelper.SeedUser(db);
+        var (game, _) = TestDbHelper.SeedGame(db, host);
+
+        var dto = await _sut.GetGameStateAsync(game.Id);
+
+        Assert.Equal(game.HostId, dto.HostUserId);
+    }
+
     // ---------- JoinGameAsync ----------
 
     [Fact]