fix(wallet): stop logging new idempotency keys as errors

GetTransactionByIdempotencyKey used First, so every wallet operation with a
key not seen before, which is the normal case, logged a "record not found"
error. It now uses Find with a limit and returns nil when nothing matches.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/repository/wallet_repository.go

@@ -188,17 +188,20 @@ func (r *walletRepository) CreateTransaction(ctx context.Context, walletTx *enti
 }
 
 func (r *walletRepository) GetTransactionByIdempotencyKey(ctx context.Context, key string) (*entities.WalletTransaction, error) {
-	var walletTx entities.WalletTransaction
+	// Find rather than First: a new key is the normal case, and First would log every
+	// one of them as a "record not found" error.
+	var walletTxs []entities.WalletTransaction
 	err := DBFromContext(ctx, r.db).WithContext(ctx).
 		Where("idempotency_key = ?", key).
-		First(&walletTx).Error
+		Limit(1).
+		Find(&walletTxs).Error
 	if err != nil {
-		if errors.Is(err, gorm.ErrRecordNotFound) {
-			return nil, nil
-		}
 		return nil, fmt.Errorf("failed to get wallet transaction by idempotency key: %w", err)
 	}
-	return &walletTx, nil
+	if len(walletTxs) == 0 {
+		return nil, nil
+	}
+	return &walletTxs[0], nil
 }
 
 func (r *walletRepository) CreateLot(ctx context.Context, lot *entities.WalletLot) error {