feat: 实现动态租户解析与移除菜单回退逻辑

1. 新增 ITenantCodeResolver 接口和 DatabaseTenantCodeResolver 实现
2. 修改 TenantResolutionMiddleware 支持从数据库动态解析租户编码
3. ITenantRepository 新增 FindIdByCodeAsync 方法
4. 移除 EfMenuRepository 中危险的系统菜单回退逻辑
5. 调整服务注册顺序确保依赖正确注入

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Modules/TakeoutSaaS.Module.Tenancy/Extensions/TenantServiceCollectionExtensions.cs

@@ -18,6 +18,7 @@ public static class TenantServiceCollectionExtensions
     {
         services.TryAddSingleton<ITenantContextAccessor, TenantContextAccessor>();
         services.TryAddScoped<ITenantProvider, TenantProvider>();
+        services.TryAddScoped<ITenantCodeResolver, DatabaseTenantCodeResolver>();
 
         services.AddOptions<TenantResolutionOptions>()
             .Bind(configuration.GetSection("Tenancy"))