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/JsonDataExtension.cs

@@ -0,0 +1,64 @@
+using LitJson;
+
+public static class JsonDataExtension
+{
+	public static bool TryGetValue(this JsonData data, string key, out JsonData value)
+	{
+		value = null;
+		if (!data.IsObject)
+		{
+			return false;
+		}
+		if (!data.Keys.Contains(key))
+		{
+			return false;
+		}
+		value = data[key];
+		return true;
+	}
+
+	public static string GetValueOrDefault(this JsonData data, string key, string defaultValue)
+	{
+		if (!data.TryGetValue(key, out var value))
+		{
+			return defaultValue;
+		}
+		return value.ToString();
+	}
+
+	public static int GetValueOrDefault(this JsonData data, string key, int defaultValue)
+	{
+		if (!data.TryGetValue(key, out var value))
+		{
+			return defaultValue;
+		}
+		return value.ToInt();
+	}
+
+	public static long GetValueOrDefault(this JsonData data, string key, long defaultValue)
+	{
+		if (!data.TryGetValue(key, out var value))
+		{
+			return defaultValue;
+		}
+		return value.ToLong();
+	}
+
+	public static double GetValueOrDefault(this JsonData data, string key, double defaultValue)
+	{
+		if (!data.TryGetValue(key, out var value))
+		{
+			return defaultValue;
+		}
+		return value.ToDouble();
+	}
+
+	public static bool GetValueOrDefault(this JsonData data, string key, bool defaultValue)
+	{
+		if (!data.TryGetValue(key, out var value))
+		{
+			return defaultValue;
+		}
+		return value.ToBoolean();
+	}
+}