feat: salvar data original da transação e data de vencimento no cartão

Ao importar fatura de cartão com PaymentDate configurado, a data efetiva
da transação passa a ser o vencimento e a data de compra é preservada em
original_date. Migration 013 adiciona a coluna original_date em transactions.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

apps/api/internal/model/transaction.go

@@ -17,13 +17,14 @@ type Transaction struct {
 
 // ImportRow is a parsed-but-not-yet-saved transaction from a file.
 type ImportRow struct {
-	Date        string  `json:"date"`
-	Amount      float64 `json:"amount"`
-	Description string  `json:"description"`
-	Type        string  `json:"type"`
-	CategoryID  *int    `json:"category_id,omitempty"`
-	ExternalID  string  `json:"external_id,omitempty"` // FITID from OFX
-	IsDuplicate bool    `json:"is_duplicate"`
+	Date         string  `json:"date"`          // effective date (payment date for credit cards)
+	OriginalDate string  `json:"original_date"` // purchase date from the CSV (empty for non-credit imports)
+	Amount       float64 `json:"amount"`
+	Description  string  `json:"description"`
+	Type         string  `json:"type"`
+	CategoryID   *int    `json:"category_id,omitempty"`
+	ExternalID   string  `json:"external_id,omitempty"` // FITID from OFX
+	IsDuplicate  bool    `json:"is_duplicate"`
 }
 
 // ImportResult is the response after confirming an import.
@@ -44,4 +45,5 @@ type CSVMapping struct {
 	FieldSeparator    string `json:"field_separator"`   // "," or ";"
 	SkipNegative      bool   `json:"skip_negative"`     // skip rows with negative amount (e.g. credit card bill payments)
 	AllExpenses       bool   `json:"all_expenses"`      // treat all rows as expense (credit card statements)
+	PaymentDate       string `json:"payment_date"`      // YYYY-MM-DD; when set, overrides date for all rows (credit card due date)
 }