Add insect surface-walker controller and mode

Add InsectController (transform-driven SphereCast surface following, no
CharacterController/Rigidbody, no gravity or slope limit) and InsectMode as a
third game mode. Wire it into GameModeManager with conditional registration so
PlayerControl and Insect modes only join the Tab cycle when their controller is
present. PaintMode/PlayerControlMode toggle the insect controller accordingly.

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

Assets/Scripts/GameModeManager.cs

@@ -22,6 +22,9 @@ public class GameModeManager : MonoBehaviour
     [Tooltip("Mesh painter. Empty = found automatically.")]
     public MeshPainter painter;
 
+    [Tooltip("Insect / surface-walk controller. Empty = found automatically.")]
+    public InsectController insect;
+
     [Header("Switching")]
     [Tooltip("Key that cycles to the next mode.")]
 #if ENABLE_INPUT_SYSTEM
@@ -36,6 +39,7 @@ public class GameModeManager : MonoBehaviour
     public PlayerCharacterController Player => player;
     public ThirdPersonOrbitInput CameraInput => cameraInput;
     public MeshPainter Painter => painter;
+    public InsectController Insect => insect;
 
     private readonly List<GameMode> _modes = new List<GameMode>();
     private int _activeIndex = -1;
@@ -49,6 +53,7 @@ public class GameModeManager : MonoBehaviour
         if (!player) player = FindFirstObjectByType<PlayerCharacterController>();
         if (!cameraInput) cameraInput = FindFirstObjectByType<ThirdPersonOrbitInput>();
         if (!painter) painter = FindFirstObjectByType<MeshPainter>();
+        if (!insect) insect = FindFirstObjectByType<InsectController>();
 
         BuildModes();
     }
@@ -63,9 +68,19 @@ public class GameModeManager : MonoBehaviour
     private void BuildModes()
     {
         _modes.Clear();
-        _modes.Add(new PlayerControlMode());
+
+        // Player Control only joins the Tab cycle when a gravity player is present, so a scene
+        // running only the insect walker doesn't trap input in a dead, player-freezing mode.
+        if (player)
+            _modes.Add(new PlayerControlMode());
+
         _modes.Add(new PaintMode());
 
+        // Insect mode only joins the Tab cycle when a surface walker is present, so a scene
+        // without one behaves exactly as before (no dead, player-freezing mode in the cycle).
+        if (insect)
+            _modes.Add(new InsectMode());
+
         foreach (var m in _modes)
             m.Bind(this);
     }