feat(battle-engine): full Unity primitive/runtime surface + game extension copies

Grows Vector2/3, Mathf, Color, Quaternion, GameObject, Transform, Camera, Material,
ParticleSystem, Rect, Bounds, Time to the surface the engine references; adds Input/
Random/Resources statics + full KeyCode enum. Copies the verbatim extension files that
collapse thousands of CS1061s at once (ContentKeywordExt, JsonData/LitJson extensions,
EventExtension.Call, GameObjectExtension(s)). 26.5k -> 15.9k errors; residual now
dominated by god-object member surface (GameMgr/UIManager/EffectMgr/Vfx*).

SVSim.BattleEngine/Engine/GameObjectExtension.cs

@@ -0,0 +1,21 @@
+using UnityEngine;
+
+public static class GameObjectExtension
+{
+	public static void SetLayer(this GameObject gameObject, int layer, bool isSetChildren)
+	{
+		if (gameObject == null)
+		{
+			return;
+		}
+		gameObject.layer = layer;
+		if (!isSetChildren)
+		{
+			return;
+		}
+		foreach (Transform item in gameObject.transform)
+		{
+			item.gameObject.SetLayer(layer, isSetChildren);
+		}
+	}
+}