feat(vm): IHost.Sleep seam + dispatch 0xc8 (headless hosts no-op; parity held)

- IHost.Sleep(long duration); VM case "sleep" forwards the raw operand.
- 8 non-Godot hosts no-op Sleep; RecordingHost records it.
- SleepDispatchTests (51 green); sweep unchanged 284 exit / 13 STEP-LIMIT.

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

engine/Age.Engine.Tests/TestSupport.cs

@@ -10,8 +10,10 @@ internal sealed class RecordingHost : IHost
 {
     public int Waits;
     public readonly List<(int Offset, string Text)> Lines = new();
+    public readonly List<long> SleptDurations = new();
     public void ShowText(int offset, string text) => Lines.Add((offset, text));
     public void WaitForInput() => Waits++;
+    public void Sleep(long duration) => SleptDurations.Add(duration);
     public void CreateTexture(int slot, int w, int h) { }
     public void SetTexture(long resId, int slot) { }
     public void DrawTexture(int slot, int sx, int sy, int w, int h, int dx, int dy) { }