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/invoices/__tests__/payment-accounts.test.ts

@@ -3,6 +3,8 @@ import {
   InvoicePaymentAccountMissingError,
   assertInvoicePaymentAccountForRender,
   companyWithInvoicePaymentAccount,
+  describeMissingInvoicePaymentAccount,
+  isInvoicePaymentAccountCurrency,
   hasRequiredInvoicePaymentAccount,
   hasUsableInvoicePaymentAccount,
   invoiceRequiresPaymentAccount,
@@ -212,3 +214,42 @@ describe('invoice payment accounts', () => {
     expect(hasRequiredInvoicePaymentAccount(emptySettings, makeInvoice())).toBe(false)
   })
 })
+
+describe('describeMissingInvoicePaymentAccount (#2126)', () => {
+  it('SEK: names the domestic options and never talks about currency accounts', () => {
+    const { sv, en } = describeMissingInvoicePaymentAccount('SEK')
+    expect(sv).toContain('bankgiro')
+    expect(sv).toContain('plusgiro')
+    expect(sv).toContain('Swish')
+    expect(sv).toContain('Inställningar → Fakturering')
+    expect(sv).not.toMatch(/valuta/i)
+    expect(sv).not.toMatch(/IBAN/)
+    expect(en).toContain('bankgiro')
+    expect(en).toContain('Settings → Invoicing')
+    expect(en).not.toMatch(/currency/i)
+  })
+
+  it('EUR: asks for an IBAN account in that currency', () => {
+    const { sv, en } = describeMissingInvoicePaymentAccount('EUR')
+    expect(sv).toContain('EUR')
+    expect(sv).toContain('IBAN')
+    expect(sv).not.toContain('routing number')
+    expect(sv).toContain('Inställningar → Fakturering')
+    expect(en).toContain('EUR')
+    expect(en).toContain('IBAN')
+  })
+
+  it('USD/GBP: also offers the non-IBAN routing path', () => {
+    expect(describeMissingInvoicePaymentAccount('USD').sv).toContain('routing number')
+    expect(describeMissingInvoicePaymentAccount('GBP').sv).toContain('sort code')
+    expect(describeMissingInvoicePaymentAccount('GBP').en).toContain('sort code')
+  })
+
+  it('isInvoicePaymentAccountCurrency guards the details field', () => {
+    expect(isInvoicePaymentAccountCurrency('SEK')).toBe(true)
+    expect(isInvoicePaymentAccountCurrency('NOK')).toBe(true)
+    expect(isInvoicePaymentAccountCurrency('JPY')).toBe(false)
+    expect(isInvoicePaymentAccountCurrency(undefined)).toBe(false)
+    expect(isInvoicePaymentAccountCurrency(42)).toBe(false)
+  })
+})