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/SleepDispatchTests.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+using Age.Engine.Vm;
+using Xunit;
+
+public class SleepDispatchTests
+{
+    [Fact]
+    public void SleepOp_ForwardsRawOperand_ToHost_AndAdvancesLikeNoop()
+    {
+        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
+        (int, Operand[]) Sleep(long ms) => (0xc8, new[] { new Operand(0, ms) });
+        (int, Operand[]) Show(int s) => (0x6e, new[] { new Operand(2, s), new Operand(0, 0) });
+        (int, Operand[]) Exit() => (0x2, System.Array.Empty<Operand>());
+
+        var script = ScriptAssembler.Assemble(table, "SLEEPTEST",
+            new List<(int, Operand[])> { Sleep(200), Show(0), Sleep(1000), Exit() }, new[] { "hi" });
+
+        var host = new RecordingHost();
+        var vm = new VirtualMachine(script, table, host);
+        vm.Run();
+
+        Assert.Equal(new List<long> { 200, 1000 }, host.SleptDurations);
+        Assert.Single(host.Lines);                        // the show-text between the sleeps still ran
+    }
+}