Trim comments and use implicit null checks for Unity objects

Reduce comments to non-obvious "why" notes and convert UnityEngine.Object
null checks to implicit bool (if (obj) / if (!obj)). Input System devices
(Mouse.current, Keyboard.current) and plain arrays keep explicit != null.

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

Assets/Scripts/PlayerControlMode.cs

@@ -1,6 +1,6 @@
 /// <summary>
-/// Mode 1: the player walks with WASD/Space and the camera orbits freely with
-/// the mouse (cursor locked/hidden). Mesh painting is disabled.
+/// Player walks with WASD/Space, the camera orbits freely with the mouse.
+/// Painting is disabled.
 /// </summary>
 public class PlayerControlMode : GameMode
 {
@@ -8,13 +8,13 @@ public class PlayerControlMode : GameMode
 
     public override void Enter()
     {
-        if (Manager.Player != null)
+        if (Manager.Player)
             Manager.Player.ControlEnabled = true;
 
-        if (Manager.CameraInput != null)
+        if (Manager.CameraInput)
             Manager.CameraInput.LookMode = ThirdPersonOrbitInput.OrbitLookMode.AlwaysActive;
 
-        if (Manager.Painter != null)
+        if (Manager.Painter)
             Manager.Painter.PaintingEnabled = false;
     }
 }