fix: implement token invalidation on password change

backend/internal/service/user_service.go

@@ -116,6 +116,7 @@ func (s *UserService) UpdateProfile(ctx context.Context, userID int64, req Updat
 }
 
 // ChangePassword 修改密码
+// Security: Increments TokenVersion to invalidate all existing JWT tokens
 func (s *UserService) ChangePassword(ctx context.Context, userID int64, req ChangePasswordRequest) error {
 	user, err := s.userRepo.GetByID(ctx, userID)
 	if err != nil {
@@ -131,6 +132,10 @@ func (s *UserService) ChangePassword(ctx context.Context, userID int64, req Chan
 		return fmt.Errorf("set password: %w", err)
 	}
 
+	// Increment TokenVersion to invalidate all existing tokens
+	// This ensures that any tokens issued before the password change become invalid
+	user.TokenVersion++
+
 	if err := s.userRepo.Update(ctx, user); err != nil {
 		return fmt.Errorf("update user: %w", err)
 	}