refactor(hosting): drop CallScript/OnStub from IHost (now trace events)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

engine/Age.Engine.Tests/GameSessionTests.cs

@@ -28,8 +28,6 @@ public class GameSessionTests
         public int Voices;
         public List<int> Emitted = new();
         public void ShowText(int o, string t) => Emitted.Add(o);
-        public void CallScript(long id) { }
-        public void OnStub(int op) { }
         public void WaitForInput() { }
         public void CreateTexture(int s, int w, int h) { }
         public void SetTexture(long r, int s) { }