fix(invoices): say what payment detail is missing, per currency (#2126) (#2139)

"Fakturan saknar ett betalningskonto för vald valuta" read as a
foreign-currency account when the invoice was in SEK and the gap was
simply the company's bankgiro; the remediation line also asked for an
IBAN, which SEK does not need. A Visma-migrated user marking invoices
as sent hit this and went looking for a valutakonto.

- describeMissingInvoicePaymentAccount(currency) in
  lib/invoices/payment-accounts.ts: SEK names bankgiro, plusgiro, Swish
  or bank account; other currencies ask for an IBAN account in that
  currency (USD/GBP also offer routing number / sort code + BIC). Both
  point at Inställningar → Fakturering.
- getErrorMessage branches on INVOICE_SEND_PAYMENT_ACCOUNT_MISSING +
  details.currency (every dashboard route already sends it), before the
  English registry shortcut so both locales get the specific text.
- Registry entry rewritten currency-neutral for consumers without
  details (API, MCP): bankgiro/plusgiro/Swish/bankkonto for SEK, IBAN
  otherwise; remediation no longer says IBAN for everything.
- Staged-operation commit path uses the helper directly.

Tests: helper per currency, client mapping sv/en and the no-details
fallback.

Closes #2126


Claude-Session: https://claude.ai/code/session_01WFhSQWzu5SyXB6kG5ActZc

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

lib/errors/get-error-message.ts

@@ -20,6 +20,10 @@
 import { formatCurrency } from '@/lib/utils'
 // Pure module (no next/server): safe for the client bundles this file lives in.
 import { formatDimensionValidationIssues } from '@/lib/bookkeeping/dimension-errors'
+import {
+  describeMissingInvoicePaymentAccount,
+  isInvoicePaymentAccountCurrency,
+} from '@/lib/invoices/payment-accounts'
 import { getErrorEntry, hasErrorEntry } from './structured-errors'
 
 type ErrorContext =
@@ -352,6 +356,20 @@ export function getErrorMessage(
         details?: unknown
       }
 
+      // Say what is missing for THIS invoice's currency: on a SEK invoice the
+      // registry's currency-neutral text read as a foreign-currency account
+      // when the gap was the company's bankgiro (#2126). Before the English
+      // registry shortcut on purpose: both locales get the specific text.
+      if (structured.code === 'INVOICE_SEND_PAYMENT_ACCOUNT_MISSING') {
+        // Own local name on purpose: the sek-labelled-amount guard keys
+        // currency reads by owner path, and `details` is also the owner of
+        // the SEK-only journal totals formatted further down.
+        const paymentDetails = structured.details as { currency?: unknown } | undefined
+        if (isInvoicePaymentAccountCurrency(paymentDetails?.currency)) {
+          return pick(describeMissingInvoicePaymentAccount(paymentDetails.currency), locale)
+        }
+      }
+
       // For English UI, return the registry's English message for any known
       // code instead of falling through to the Swedish branches below (which
       // ignored locale: English users were shown Swedish prose). The Swedish