fix: 租户端启动补齐字典与消息依赖

src/Modules/TakeoutSaaS.Module.Messaging/Extensions/MessagingServiceCollectionExtensions.cs

@@ -17,8 +17,17 @@ public static class MessagingServiceCollectionExtensions
     /// </summary>
     public static IServiceCollection AddMessagingModule(this IServiceCollection services, IConfiguration configuration)
     {
+        var rabbitMqSection = configuration.GetSection("RabbitMQ");
+        if (!rabbitMqSection.Exists())
+        {
+            services.AddSingleton<IMessagePublisher, NoOpMessagePublisher>();
+            services.AddSingleton<IMessageSubscriber, NoOpMessageSubscriber>();
+            return services;
+        }
+
+        // 1. (空行后) 存在 RabbitMQ 配置时才启用真实 MQ 能力（启动时验证配置完整性）
         services.AddOptions<RabbitMqOptions>()
-            .Bind(configuration.GetSection("RabbitMQ"))
+            .Bind(rabbitMqSection)
             .ValidateDataAnnotations()
             .ValidateOnStart();