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/TextureOpsTests.cs.bak

@@ -0,0 +1,36 @@
+using System.Collections.Generic;
+using Age.Engine.Hosting;
+using Age.Engine.Sys4;
+using Age.Engine.Vm;
+using Xunit;
+
+public class TextureOpsTests
+{
+    private sealed class RecHost : IHost
+    {
+        public List<(long resId, int slot)> Sets = new();
+        public List<(int slot, int w, int h)> Draws = new();
+        public int Creates;
+        public void ShowText(int o, string t) { }
+        public void WaitForInput() { }
+        public void CreateTexture(int slot, int w, int h) => Creates++;
+        public void SetTexture(long resId, int slot) => Sets.Add((resId, slot));
+        public void DrawTexture(int slot, int srcX, int srcY, int w, int h, int dstX, int dstY) => Draws.Add((slot, w, h));
+        public (int Width, int Height) GetTextureSize(int slot) => (0, 0);
+        public void PlayBgm(long id) { }
+        public void PlayVoice(long id) { }
+    }
+
+    [Fact]
+    public void SC0000FiresTextureOpsWithSlot0FullScreenSlideshow()
+    {
+        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
+        var script = Sys4Loader.Load(Paths.Scripts()["SC0000.BIN"], table);
+        var host = new RecHost();
+        new VirtualMachine(script, table, host).Run();
+        Assert.True(host.Creates > 0, "create-texture should fire");
+        // The intro loads a sequence of full-screen images into slot 0; res 0x23 is the first bg.
+        Assert.Contains(host.Sets, s => s.resId == 0x23 && s.slot == 0);
+        Assert.Contains(host.Draws, d => d.slot == 0 && d.w == 0x320 && d.h == 0x258);
+    }
+}