feat: finalize core modules and gateway

src/Application/TakeoutSaaS.Application/Messaging/EventRoutingKeys.cs

@@ -0,0 +1,17 @@
+namespace TakeoutSaaS.Application.Messaging;
+
+/// <summary>
+/// 事件路由键常量。
+/// </summary>
+public static class EventRoutingKeys
+{
+    /// <summary>
+    /// 订单创建事件路由键。
+    /// </summary>
+    public const string OrderCreated = "orders.created";
+
+    /// <summary>
+    /// 支付成功事件路由键。
+    /// </summary>
+    public const string PaymentSucceeded = "payments.succeeded";
+}