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/ContentKeywordExt.cs

@@ -0,0 +1,14 @@
+internal static class ContentKeywordExt
+{
+	public static string ToStringCustom(this SkillFilterCreator.ContentKeyword type)
+	{
+		return type switch
+		{
+			SkillFilterCreator.ContentKeyword._class => "class", 
+			SkillFilterCreator.ContentKeyword._true => "true", 
+			SkillFilterCreator.ContentKeyword._false => "false", 
+			SkillFilterCreator.ContentKeyword._ref_prev => "<-", 
+			_ => type.ToString(), 
+		};
+	}
+}