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/__tests__/get-error-message.test.ts

@@ -563,3 +563,41 @@ describe('getProviderResourceForbiddenMessage', () => {
     expect(getProviderResourceForbiddenMessage(null)).not.toMatch(/återanslut för att fortsätta/i)
   })
 })
+
+describe('getErrorMessage: INVOICE_SEND_PAYMENT_ACCOUNT_MISSING (#2126)', () => {
+  const envelope = (currency?: unknown) => ({
+    error: {
+      code: 'INVOICE_SEND_PAYMENT_ACCOUNT_MISSING',
+      message: getErrorEntry('INVOICE_SEND_PAYMENT_ACCOUNT_MISSING')!.message_sv,
+      message_en: getErrorEntry('INVOICE_SEND_PAYMENT_ACCOUNT_MISSING')!.message_en,
+      ...(currency !== undefined ? { details: { currency } } : {}),
+    },
+  })
+
+  it('SEK invoice: names bankgiro/plusgiro/Swish, not a currency account', () => {
+    const msg = getErrorMessage(envelope('SEK'), { statusCode: 400 })
+    expect(msg).toContain('bankgiro')
+    expect(msg).toContain('Inställningar → Fakturering')
+    expect(msg).not.toMatch(/valuta/i)
+  })
+
+  it('EUR invoice: asks for an IBAN account for EUR', () => {
+    const msg = getErrorMessage(envelope('EUR'), { statusCode: 400 })
+    expect(msg).toContain('EUR')
+    expect(msg).toContain('IBAN')
+  })
+
+  it('English locale gets the currency-specific English text, not the registry fallback', () => {
+    const msg = getErrorMessage(envelope('SEK'), { statusCode: 400, locale: 'en' })
+    expect(msg).toContain('bankgiro')
+    expect(msg).toContain('Settings → Invoicing')
+    expect(msg).not.toMatch(/currency/i)
+  })
+
+  it('without a currency in details, falls back to the registry text', () => {
+    const msg = getErrorMessage(envelope(), { statusCode: 400 })
+    expect(msg).toBe(getErrorEntry('INVOICE_SEND_PAYMENT_ACCOUNT_MISSING')!.message_sv)
+    const unknown = getErrorMessage(envelope('JPY'), { statusCode: 400 })
+    expect(unknown).toBe(getErrorEntry('INVOICE_SEND_PAYMENT_ACCOUNT_MISSING')!.message_sv)
+  })
+})