为 9 个模块添加 Context 超时控制

完成模块：
- auth: 3 个 Repository 方法 + Service + Handler + Middleware
- wallet: 已有 context 支持，修复依赖调用
- payment: 已有 context 支持，修复 wallet 调用
- adminaudit: 1 个方法
- notification: 2 个方法
- realname: 2 个方法
- systemconfig: 4 个方法
- adminauth: 7 个方法
- adminuser: 6 个方法

所有数据库调用已改为 r.db.WithContext(ctx)，完整传递 context 链路。

待完成模块: order, listing, chat 等 12 个模块（约 157 个方法）

backend/internal/modules/adminuser/service.go

@@ -1,6 +1,9 @@
 package adminuser
 
-import "errors"
+import (
+	"context"
+	"errors"
+)
 
 var (
 	ErrDependencyUnavailable = errors.New("dependency unavailable")
@@ -15,39 +18,39 @@ func NewService(repo *Repository) *Service {
 	return &Service{repo: repo}
 }
 
-func (s *Service) List(page, pageSize int) (*PaginatedResult, error) {
+func (s *Service) List(ctx context.Context, page, pageSize int) (*PaginatedResult, error) {
 	if s.repo == nil {
 		return nil, ErrDependencyUnavailable
 	}
-	return s.repo.List(page, pageSize)
+	return s.repo.List(ctx, page, pageSize)
 }
 
-func (s *Service) Freeze(adminID uint64, userID uint64, req FreezeRequest, meta AuditMeta) (*UserDTO, error) {
+func (s *Service) Freeze(ctx context.Context, adminID uint64, userID uint64, req FreezeRequest, meta AuditMeta) (*UserDTO, error) {
 	if s.repo == nil {
 		return nil, ErrDependencyUnavailable
 	}
 	if userID == 0 {
 		return nil, ErrInvalidUser
 	}
-	return s.repo.Freeze(adminID, userID, req, meta)
+	return s.repo.Freeze(ctx, adminID, userID, req, meta)
 }
 
-func (s *Service) Unfreeze(adminID uint64, userID uint64, meta AuditMeta) (*UserDTO, error) {
+func (s *Service) Unfreeze(ctx context.Context, adminID uint64, userID uint64, meta AuditMeta) (*UserDTO, error) {
 	if s.repo == nil {
 		return nil, ErrDependencyUnavailable
 	}
 	if userID == 0 {
 		return nil, ErrInvalidUser
 	}
-	return s.repo.Unfreeze(adminID, userID, meta)
+	return s.repo.Unfreeze(ctx, adminID, userID, meta)
 }
 
-func (s *Service) SetDepositFreeQuota(adminID uint64, userID uint64, req DepositFreeQuotaRequest, meta AuditMeta) (*UserDTO, error) {
+func (s *Service) SetDepositFreeQuota(ctx context.Context, adminID uint64, userID uint64, req DepositFreeQuotaRequest, meta AuditMeta) (*UserDTO, error) {
 	if s.repo == nil {
 		return nil, ErrDependencyUnavailable
 	}
 	if userID == 0 || req.AmountCent < 0 {
 		return nil, ErrInvalidUser
 	}
-	return s.repo.SetDepositFreeQuota(adminID, userID, req, meta)
+	return s.repo.SetDepositFreeQuota(ctx, adminID, userID, req, meta)
 }