fix(salary): make pain.001 betalfil generatable (company IBAN + BIC) (#950)

The ISO 20022 pain.001 salary payment file could never be generated: the
route required company_settings.iban/bic, but no settings screen wrote
those columns, so every request returned 400. The specific reason was
also swallowed by getErrorMessage (isSwedishUserMessage did not know
"krävs"/"saknar"), surfacing only the generic "Förfrågan innehåller
ogiltiga uppgifter" (issue #945).

- Add IBAN + BIC inputs to Settings > Fakturering > Bankuppgifter. BIC
  auto-derives from the clearing number / bank already entered, so in
  practice only the IBAN is typed. Validated client- and server-side.
- Route requires the company IBAN (canonical debtor form every Swedish
  bank accepts) and derives the BIC, with clear actionable errors.
- Employees are unchanged: domestic clearing + account (BBAN), which is
  what Swedish payroll collects. Only the company (debtor) uses IBAN.
- getErrorMessage recognizes "krävs"/"saknar" so payment-file reasons
  surface instead of the generic 400.

Fixes #945

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -147,6 +147,38 @@ describe('getErrorMessage: accumulated validation details', () => {
   })
 })
 
+describe('getErrorMessage: payment-file route messages surface (issue #945)', () => {
+  // These specific { error: '...' } strings previously collapsed to the generic
+  // HTTP-400 message because isSwedishUserMessage did not recognize "krävs" /
+  // "saknar", so the user learned nothing about why the betalfil failed.
+  it('surfaces a "saknar bankkontouppgifter" message instead of the generic 400', () => {
+    const msg = getErrorMessage(
+      { error: '2 anställd(a) saknar bankkontouppgifter' },
+      { context: 'salary', statusCode: 400 },
+    )
+    expect(msg).toBe('2 anställd(a) saknar bankkontouppgifter')
+    expect(msg).not.toBe('Förfrågan innehåller ogiltiga uppgifter.')
+  })
+
+  it('surfaces a "... krävs ..." message instead of the generic 400', () => {
+    const msg = getErrorMessage(
+      { error: 'Momsregistreringsnummer krävs när företaget är momsregistrerat (ML 11 kap. 8§)' },
+      { context: 'settings', statusCode: 400 },
+    )
+    expect(msg).toContain('krävs')
+    expect(msg).not.toBe('Förfrågan innehåller ogiltiga uppgifter.')
+  })
+
+  it('surfaces the missing company bank-account message', () => {
+    const msg = getErrorMessage(
+      { error: 'Företagets bankkonto (clearingnummer och kontonummer) saknas i företagsinställningar. Fyll i det under Inställningar → Fakturering för att skapa betalfil.' },
+      { context: 'salary', statusCode: 400 },
+    )
+    expect(msg).toContain('Företagets bankkonto')
+    expect(msg).not.toBe('Förfrågan innehåller ogiltiga uppgifter.')
+  })
+})
+
 describe('getErrorMessage: existing patterns still work', () => {
   it('regex match for "Entry date ... outside fiscal period" on plain string', () => {
     const msg = getErrorMessage('Entry date 2024-06-15 is outside fiscal period "FY 2025"')

lib/errors/get-error-message.ts

@@ -166,6 +166,8 @@ function isSwedishUserMessage(message: string): boolean {
     /försök igen/i,
     /ogiltigt?/i,
     /saknas/i,
+    /saknar/i,
+    /krävs/i,
     /måste/i,
     /redan finns/i,
     /gick fel/i,