cull(engine-cleanup): pass-8 phase-2 cascade round 1

[trim] fully-unreachable files deleted: 6
[trim] files edited: 55, files deleted: 0, nodes removed: 244
[type-trim] files edited: 1, types removed: 1

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.BattleEngine/Engine/InputMgr.cs

@@ -64,18 +64,6 @@ public class InputMgr
 
 	private ClickState _clickState;
 
-	public bool isBackKeyEnable
-	{
-		get
-		{
-			return _isBackKeyEnable;
-		}
-		set
-		{
-			_isBackKeyEnable = value;
-		}
-	}
-
 	public bool WentOverDrag
 	{
 		get