feat(gfx): GfxState animation-channel model (per-object transform + global clock)

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

engine/Age.Engine.Tests/GfxAnimationTests.cs

@@ -0,0 +1,45 @@
+using System.Collections.Generic;
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+using Age.Engine.Vm;
+using Xunit;
+
+public class GfxAnimationTests
+{
+    // ---- Task 2: GfxState animation-channel data model (revised global-clock model, see engine-re.md) ----
+
+    [Fact]
+    public void SetAnimTransform_RecordsTargetParamsAndEnables()
+    {
+        var g = new GfxState();
+        g.SetAnimTransform(0x1000, p1: 7, p2: 9, target: (100, 100, 100), normalized: true);
+        var o = g.TryGet(0x1000)!;
+        Assert.Equal((100L, 100L, 100L), o.AnimTarget);
+        Assert.Equal(7, o.AnimParam1);
+        Assert.Equal(9, o.AnimParam2);
+        Assert.True(o.AnimNormalized);
+        Assert.True(o.AnimEnabled);
+    }
+
+    [Fact]
+    public void StartAnim_SetsTargetDurationEnablesAndBumpsGeneration()
+    {
+        var g = new GfxState();
+        g.StartAnim(0x1000, durationTicks: 30, target: (0, 0, 5));
+        var o = g.TryGet(0x1000)!;
+        Assert.Equal((0L, 0L, 5L), o.AnimTarget);
+        Assert.Equal(30, o.AnimDurationTicks);
+        Assert.True(o.AnimEnabled);
+        Assert.Equal(1, o.AnimGeneration);      // fresh object starts at 0, one anim-start -> 1
+    }
+
+    [Fact]
+    public void SetAnimClock_SetsGlobalDurationAndBumpsClockGeneration()
+    {
+        var g = new GfxState();
+        var cg0 = g.AnimClockGeneration;
+        g.SetAnimClock(400);
+        Assert.Equal(400, g.AnimClockDurationTicks);
+        Assert.Equal(cg0 + 1, g.AnimClockGeneration);
+    }
+}