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/Infrastructure/TakeoutSaaS.Infrastructure/App/Repositories/EfTenantRepository.cs

@@ -162,6 +162,20 @@ public sealed class EfTenantRepository(TakeoutAppDbContext context, TakeoutLogsD
         return context.Tenants.AnyAsync(x => x.Code == normalized, cancellationToken);
     }
 
+    /// <inheritdoc />
+    public Task<long?> FindIdByCodeAsync(string code, CancellationToken cancellationToken = default)
+    {
+        // 1. 标准化编码
+        var normalized = code.Trim();
+
+        // 2. 查询租户 ID（仅查询未删除且状态正常的租户）
+        return context.Tenants
+            .AsNoTracking()
+            .Where(x => x.Code == normalized && x.DeletedAt == null)
+            .Select(x => (long?)x.Id)
+            .FirstOrDefaultAsync(cancellationToken);
+    }
+
     /// <inheritdoc />
     public Task<bool> ExistsByNameAsync(string name, long? excludeTenantId = null, CancellationToken cancellationToken = default)
     {