功能：优化账号分层与管理员初始化

backend/internal/service/user.go

@@ -7,6 +7,7 @@ import (
 
 	"golang.org/x/crypto/bcrypt"
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
 )
 
 type UserService struct {
@@ -58,6 +59,23 @@ func (s *UserService) List(q UserListQuery) ([]model.User, int64, error) {
 	return list, total, err
 }
 
+// ListMerchantMembers returns employee assignments across merchants for platform operations.
+func (s *UserService) ListMerchantMembers(page, size int) ([]model.MerchantMember, int64, error) {
+	page, size = normalizePage(page, size)
+	tx := s.db.Model(&model.MerchantMember{}).
+		Joins("JOIN users ON users.id = merchant_members.user_id AND users.deleted_at IS NULL").
+		Where("users.role = ?", model.RoleMerchant)
+	var total int64
+	if err := tx.Count(&total).Error; err != nil {
+		return nil, 0, err
+	}
+	var members []model.MerchantMember
+	err := tx.Preload("Merchant").Preload("User").
+		Order("merchant_members.merchant_id ASC, merchant_members.id ASC").
+		Offset((page - 1) * size).Limit(size).Find(&members).Error
+	return members, total, err
+}
+
 func (s *UserService) Create(username, password, nickname, role string, merchantID uint) (*model.User, error) {
 	var count int64
 	s.db.Model(&model.User{}).Where("username = ?", username).Count(&count)
@@ -137,6 +155,58 @@ func (s *UserService) UpdateStatus(id uint, status int) error {
 	})
 }
 
+// UpdateRole changes the platform-level account role. Promoted administrators are
+// also made owners of the self-operated merchant for a consistent merchant context.
+func (s *UserService) UpdateRole(id uint, role string, actorUserID uint) error {
+	if id == 0 {
+		return errors.New("用户不存在")
+	}
+	if id == actorUserID {
+		return errors.New("不能修改当前登录账号的系统角色")
+	}
+	if role != model.RoleAdmin && role != model.RoleMerchant {
+		return errors.New("无效的账号角色")
+	}
+	return s.db.Transaction(func(tx *gorm.DB) error {
+		var user model.User
+		if err := tx.First(&user, id).Error; err != nil {
+			if errors.Is(err, gorm.ErrRecordNotFound) {
+				return errors.New("用户不存在")
+			}
+			return err
+		}
+		if user.Role == role {
+			return nil
+		}
+		if user.Role == model.RoleAdmin && user.Status == 1 && role != model.RoleAdmin {
+			var admins int64
+			if err := tx.Model(&model.User{}).Where("role = ? AND status = ?", model.RoleAdmin, 1).Count(&admins).Error; err != nil {
+				return err
+			}
+			if admins <= 1 {
+				return errors.New("至少保留一个启用的平台管理员")
+			}
+		}
+		if err := tx.Model(&user).Update("role", role).Error; err != nil {
+			return err
+		}
+		if role != model.RoleAdmin {
+			return nil
+		}
+		var merchant model.Merchant
+		if err := tx.Where("code = ?", model.MerchantCodeSelfOperated).First(&merchant).Error; err != nil {
+			return err
+		}
+		member := model.MerchantMember{MerchantID: merchant.ID, UserID: user.ID, Role: model.MemberRoleOwner, Status: user.Status, IsDefault: true}
+		return tx.Clauses(clause.OnConflict{
+			Columns: []clause.Column{{Name: "merchant_id"}, {Name: "user_id"}},
+			DoUpdates: clause.Assignments(map[string]interface{}{
+				"role": model.MemberRoleOwner, "status": user.Status, "is_default": true,
+			}),
+		}).Create(&member).Error
+	})
+}
+
 // Delete removes a platform account and its merchant memberships. It protects the current
 // account and the final enabled platform administrator so the platform cannot be locked out.
 func (s *UserService) Delete(id, actorUserID uint) error {