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/Hosting/CaptureHost.cs

@@ -4,6 +4,7 @@ public sealed class CaptureHost : IHost
     public List<(int Offset, string Text)> Emitted { get; } = new();
     public void ShowText(int offset, string text) => Emitted.Add((offset, text));
     public void WaitForInput() { }
+    public void Sleep(long duration) { }
     public void CreateTexture(int slot, int width, int height) { }
     public void SetTexture(long resourceId, int slot) { }
     public void DrawTexture(int slot, int srcX, int srcY, int width, int height, int dstX, int dstY) { }