fix(n+1): 批量查询替代循环单查

- IsAdminBootstrapRequired: userRepo.GetByID 循环 → GetByIDs 批量
- AssignRoles: roleRepo.GetByID 循环 → GetByIDs 批量
- 在 userRepositoryInterface 补充 GetByIDs 方法签名

internal/server/server.go

@@ -148,6 +148,9 @@ func Serve(cfg *config.Config) error {
 
 	// 初始化中间件
 	rateLimitMiddleware := middleware.NewRateLimitMiddleware(cfg.RateLimit)
+	stopRateLimitCleanup := rateLimitMiddleware.StartCleanup()
+	defer stopRateLimitCleanup()
+
 	authMiddleware := middleware.NewAuthMiddleware(
 		jwtManager,
 		userRepo,