fix(arsredovisning): unblock the signing flow, accept foreign parent org nr, explain Fortnox underlag failures (#1738)

Batch from a real migration walkthrough (Fortnox -> Accounted, 2026-08-20):

- Årsredovisning: the "Låst version" select was empty with no explanation
  because the only version was a draft and "Lås version för underskrift"
  is disabled while the four Lagstadgade upplysningar checkboxes and the
  content confirmation count as blockers. The select is now disabled with a
  hint that names the blocker count and links to Fullständighetskontroll,
  the four AR-NOTE-*-UNCONFIRMED issues carry remediation text, the lock
  button explains why it is grey, and "Markera som signerad" says what it
  still needs (locked version, bevisreferens, date).
- Moderföretagets org.nr accepts a foreign registration identifier
  (CHE-123.456.789, HRB 12345, 923 609 016); personnummer shapes stay out.
- Fortnox underlag discovery: log status, body and Fortnox's message on
  failure, show the message in the UI, treat a 400 with behörighet/scope
  text as scopes-required, and fall back to an unfiltered
  voucherfileconnections list when the financialyear filter answers 400.
- Kontomapping: the Momskod column had min-w only; table-fixed collapsed it
  and its selects overflowed into Konfidens. Real w-72 now.
- SIE import warnings pluralise correctly for one skipped voucher; the
  Verifikationsserie option says the source series is preserved.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

components/import/AccountMappingStep.tsx

@@ -248,7 +248,10 @@ export default function AccountMappingStep({
                   <TableHead className="w-64 max-w-64">Källnamn</TableHead>
                   <TableHead className="w-12"></TableHead>
                   <TableHead className="w-64">Målkonto</TableHead>
-                  <TableHead className="min-w-72">{t('vat_treatment_column')}</TableHead>
+                  {/* table-fixed sizes columns from the header's width only:
+                      min-w collapsed this column to nothing on laptop widths
+                      and its selects overflowed into Konfidens (2026-08-20). */}
+                  <TableHead className="w-72">{t('vat_treatment_column')}</TableHead>
                   <TableHead className="w-24">Konfidens</TableHead>
                   <TableHead className="sticky right-0 z-20 w-32 min-w-32 border-l border-border bg-background text-right">
                     {t('vat_treatment_confirm')}