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/Vm/VirtualMachine.cs

@@ -208,6 +208,8 @@ public sealed class VirtualMachine
                 }
                 return pc + 1;
             case "wait-for-input": _host.WaitForInput(); return pc + 1;
+            case "sleep":   // 0xc8 (duration) — pause the host duration ms; headless hosts no-op (parity). Frame pacing.
+                _host.Sleep(Read(a[0])); return pc + 1;
             case "end-text-line": case "set-font":
             case "comment": case "display-furigana": case "dev_ukn":
                 return pc + 1;