add internal gorm erros

internal/user/gorm_store.go

@@ -1,6 +1,7 @@
 package user
 
 import (
+	"errors"
 	"fmt"
 
 	"gorm.io/gorm"
@@ -24,6 +25,7 @@ func (s *GormUserStore) Create(user *User) error {
 }
 
 // Search returns a user by username or id or email
+// May return [ErrUserNotFound] if user not found
 func (s *GormUserStore) GetBy(by, value string) (*User, error) {
 	if by != "username" && by != "id" && by != "email" {
 		return nil, fmt.Errorf("unsuppored field %s", by)
@@ -31,7 +33,10 @@ func (s *GormUserStore) GetBy(by, value string) (*User, error) {
 	var user User
 	err := s.db.Where(fmt.Sprintf("%s = ?", by), value).First(&user).Error
 	if err != nil {
-		return nil, err
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			return nil, ErrUserNotFound
+		}
+		return nil, fmt.Errorf("failed to get user: %w", err)
 	}
 	return &user, nil
 }