Host the avatar test as a test suite; drop visual_novel_core dependency

- The Live2D avatar integration test (driver, overlay, test model "ren")
  moves here from the separate live2d_test mod as test_suites/avatar. It
  is mounted as the virtual mod live2d__avatar only with
  --itest=live2d_avatar; normal launches never load it.
- The runtime library needs only the interface mod; the content mod
  dependency is gone.

test_suites/avatar/src/Live2DOverlay.cs

@@ -0,0 +1,109 @@
+using Cthangover.Core.UI;
+using Cthangover.Core.Utils;
+using Cthangover.Live2D.Cubism.Framework;
+using Cthangover.Live2D.Cubism.Services;
+using Godot;
+
+using Cthangover.Mods.Interface.Base.Lists;
+namespace Mods.Live2DTest
+{
+    /// <summary>
+    /// Scene-driven replacement for the old live2d_test subscription snippet.
+    /// The overlay root is added to a shell slot by <see cref="UiHost"/>; it
+    /// spawns the Cubism model into the <c>Lastground</c> anchor and keeps a
+    /// transparent drag handle on top so the player can steer the model's head
+    /// parameters with the mouse. Created per <c>home_outside</c> visit
+    /// (once=false) and destroyed together with the overlay.
+    /// </summary>
+    public partial class Live2DOverlay : ModWidget
+    {
+        private const string ModelPath = "models/runtime/ren.model3.json";
+        private const string ModelNodeName = "Live2DTestModel";
+        private const string ContainerNodeName = "Lastground";
+
+        private CubismModelNode model;
+        private ColorRect dragHandle;
+        private bool dragging;
+        private float mouseStartX;
+        private float mouseStartY;
+        private float baseValueX;
+        private float baseValueY;
+
+        protected override void Construct()
+        {
+            MouseFilter = MouseFilterEnum.Ignore;
+
+            var container = UiHost.Instance?.FindNode(ContainerNodeName);
+            if (container == null)
+            {
+                GameLogger.Log("LIVE2D_TEST", $"Live2DOverlay: container '{ContainerNodeName}' not found", LogLevel.Error);
+                return;
+            }
+
+            model = Live2DService.CreateModel(container, ModelPath, ModelNodeName, "live2d__avatar");
+            if (model == null)
+            {
+                GameLogger.Log("LIVE2D_TEST", "Live2DOverlay: model creation failed", LogLevel.Error);
+                return;
+            }
+
+            dragHandle = new ColorRect
+            {
+                Name = "Live2DDragPanel",
+                MouseFilter = MouseFilterEnum.Stop,
+                Color = new Color(0, 1f, 0, 0f),
+                Size = new Vector2(400, 400),
+                AnchorLeft = 0.5f,
+                AnchorRight = 0.5f,
+                AnchorTop = 0.5f,
+                AnchorBottom = 0.5f,
+                OffsetLeft = -200f,
+                OffsetRight = 200f,
+                OffsetTop = -200f,
+                OffsetBottom = -200f
+            };
+            AddChild(dragHandle);
+            dragHandle.GuiInput += OnDragInput;
+        }
+
+        protected override void Destruct()
+        {
+            if (model != null && GodotObject.IsInstanceValid(model))
+                model.QueueFree();
+            model = null;
+        }
+
+        private void OnDragInput(InputEvent @event)
+        {
+            if (@event is InputEventMouseButton mb && mb.ButtonIndex == MouseButton.Left)
+            {
+                if (mb.Pressed)
+                {
+                    dragging = true;
+                    mouseStartX = mb.GlobalPosition.X;
+                    mouseStartY = mb.GlobalPosition.Y;
+                    baseValueX = model.FindParameter("ParamAngleX")?.Value ?? 0f;
+                    baseValueY = model.FindParameter("ParamAngleY")?.Value ?? 0f;
+                }
+                else
+                {
+                    dragging = false;
+                }
+                return;
+            }
+
+            if (!dragging || @event is not InputEventMouseMotion mm || model == null)
+                return;
+
+            var targetX = model.FindParameter("ParamAngleX");
+            var targetY = model.FindParameter("ParamAngleY");
+            var deltaX = (mm.GlobalPosition.X - mouseStartX) / 30f;
+            var deltaY = (mm.GlobalPosition.Y - mouseStartY) / 30f;
+
+            if (targetX != null)
+                model.SetLiveParameter("ParamAngleX", Mathf.Clamp(baseValueX + deltaX, targetX.MinimumValue, targetX.MaximumValue));
+            if (targetY != null)
+                model.SetLiveParameter("ParamAngleY", Mathf.Clamp(baseValueY + deltaY, targetY.MinimumValue, targetY.MaximumValue));
+        }
+    }
+}