fix(admin): shorten the receipt letter, show the account id

The receipt letter repeated what the receipt itself states. It now carries the
amount, the moment of payment with its offset, and the link — the receipt is
the document, and it opens without authentication, so there is nothing for the
two to disagree about. Subject reworded to name what it is.

The ledger and tax-export tables labelled the account link "card", meaning the
user card. On pages about payments that reads as a bank card, which is exactly
how it was misread. Both now show the first eight characters of the account id,
so the column carries data — two rows from the same buyer are visible at a
glance — while the link still holds the whole id.

backend/internal/mynalogsync/mailer.go

@@ -164,7 +164,7 @@ func (m *Mailer) sendReceiptMails(ctx context.Context, cancelled bool) {
 			m.stampReceipt(ctx, mark, r.LedgerID)
 			continue
 		}
-		subject, body := "Эрудит — чек от налоговой", receiptText(r, stored.INN, m.baseURL, m.loc)
+		subject, body := "Эрудит — Ваш чек покупки", receiptText(r, stored.INN, m.baseURL, m.loc)
 		if cancelled {
 			subject, body = "Эрудит — чек аннулирован", cancelText(r, m.loc)
 		}
@@ -232,19 +232,19 @@ func purchaseText(p payments.PurchaseMail) string {
 
 // receiptText is the fiscal receipt letter, which is how the receipt is actually handed to the
 // buyer as the professional-income tax regime requires.
+//
+// It is deliberately bare: the amount, the moment of payment with its offset, and the link. The
+// receipt itself is the document and it opens without authentication, so repeating its contents
+// here would only add something for the two to disagree about.
 func receiptText(r payments.ReceiptMail, inn, baseURL string, loc *time.Location) string {
 	return fmt.Sprintf(`Здравствуйте!
 
-По вашей покупке сформирован чек в налоговой службе.
+Покупка на сумму: %s от %s
+Ссылка на чек: %s
 
-%s
-Дата: %s
-Чек: %s
-
-Продавец применяет налог на профессиональный доход; чек сформирован в сервисе
-«Мой налог» Федеральной налоговой службы.
-`, describe(r.Title, r.AmountMinor, r.Currency),
-		r.OperationTime.In(loc).Format("02.01.2006 15:04"),
+Спасибо, что играете в «Эрудит».
+`, formatAmount(r.AmountMinor, r.Currency),
+		r.OperationTime.In(loc).Format("02.01.2006 15:04 -07:00"),
 		mynalog.ReceiptURL(baseURL, inn, r.ReceiptUUID))
 }