Trading: shop kind and trade.open schema; trade test passes the RPG Plus prologue

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

locale/schema_ja.properties

@@ -0,0 +1,11 @@
+trading/schema/builtin/trade_open = 店を開く
+trading/schema/builtin/trade_open_desc = その商人との交易ウィンドウ
+trading/schema/field/shop = 店
+trading/schema/kind/shop = 店
+trading/schema/kind/shop_desc = 商人が売るもの・買うもの
+trading/schema/field/name = 名前
+trading/schema/field/currency = 通貨
+trading/schema/field/sells = 売る品
+trading/schema/field/item = アイテム
+trading/schema/field/price = 価格
+trading/schema/field/buys = 買う品