fix(settings): scope cross-field VAT validations to saves that touch them (#2121)

* fix(settings): scope cross-field VAT validations to saves that touch them

The settings PUT validated the whole effective record on every partial
update, so companies stored as vat_registered without a vat_number were
blocked from saving anything through the endpoint, including the invoice
bank-details dialog, which has no VAT fields (reported by a user stuck on
"Momsregistreringsnummer kravs...").

Each cross-field check (VAT completeness, 40m-monthly, periodisk
sammanstallning) now runs only when the request body touches a field in
its group, so the invariant still holds whenever VAT config is edited.
Explicit null now counts as clearing a value during validation instead of
falling back to the stored one, closing a latent hole where
{ vat_number: null } passed validation but wrote null.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016fjJLUucErb1ZHyQ57fe1u

* fix(invoices): gate issuance on the seller VAT number (skeptic finding)

The settings scoping in the previous commit removed what was accidentally
the only enforcement of "momsregistrerad implies momsregnr on file": with
bank details saveable again, a registered company without a stored VAT
number could issue a faktura charging moms with no seller VAT number in
the footer (mandatory element, ML (2023:200) 17 kap. 24 §).

Issuance is now gated the same way the payment account is, at all four
independent issuance points (issueAndBookInvoice, dashboard send, v1 send,
v1 mark-sent), with a structured error pointing at Installningar -> Skatt.
Credit notes, proformas, and delivery notes are exempt like the payment
gate exempts them.

Also, per the Swedish review and the secondary skeptic finding:
- PS/EU-trade edits join the VAT-completeness touch group, so enabling
  periodisk sammanstallning on an incomplete registration keeps failing.
- The stale ML 11 kap. 8 citation is updated to ML 17 kap. 24.

The makeCompanySettings fixture now models a coherent registered company
(vat_number set); the missing-number tests override it explicitly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016fjJLUucErb1ZHyQ57fe1u

* fix(invoices): extend the seller-VAT-number gate to the headless issuance paths

Skeptic round 2 found three more issuance points beside the four gated in
the previous commit: the recurring auto-send service (cron, no human in
the loop), and the MCP staged-operation executors send_invoice and
mark_invoice_sent. Each carried the payment-account gate but not the VAT
gate; mark_invoice_sent additionally had a narrow settings select that
would have made a naive gate silently pass, now widened.

Recurring auto-send fails soft, matching its other guards: the invoice
stays a numbered draft with the standard schedule warning. The executors
return the structured Swedish message. Peppol send was verified
self-gating (BIS preflight requires the supplier VAT number).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016fjJLUucErb1ZHyQ57fe1u

* test(email): refresh brand-mail snapshots for the coherent VAT fixture

The makeCompanySettings fixture now carries a VAT number, so the invoice
and reminder mail footers correctly render the VAT line; the snapshots
predate that. Also cites ML 17 kap. 22-23 (andringsfaktura content list)
in the seller-vat-number docstring per the Swedish review suggestion,
documenting why credit notes are exempt. No behavior change.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016fjJLUucErb1ZHyQ57fe1u

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/pending-operations/commit.ts

@@ -128,6 +128,7 @@ import {
   hasRequiredInvoicePaymentAccount,
   invoiceRequiresPaymentAccount,
 } from '@/lib/invoices/payment-accounts'
+import { hasRequiredSellerVatNumber } from '@/lib/invoices/seller-vat-number'
 import {
   exceedsInvoiceEmailRecipientLimit,
   invoiceEmailRecipientCount,
@@ -2478,6 +2479,15 @@ async function commitSendInvoice(
     }
   }
 
+  if (!hasRequiredSellerVatNumber(company as CompanySettings, invoice as Invoice)) {
+    return {
+      error:
+        getErrorEntry('INVOICE_SEND_VAT_NUMBER_MISSING')?.message_sv
+        ?? 'Momsregistreringsnummer saknas i företagsinställningarna.',
+      status: 400,
+    }
+  }
+
   const recipients = resolveInvoiceEmailRecipients({
     to: customer.email,
     configuredCc: company.invoice_email_cc_addresses,
@@ -2711,7 +2721,7 @@ async function commitMarkInvoiceSent(
 
   const { data: settings, error: settingsError } = await supabase
     .from('company_settings')
-    .select('accounting_method, defer_invoice_booking, entity_type, invoice_payment_accounts, bank_name, clearing_number, account_number, bankgiro, plusgiro, swish, iban, bic')
+    .select('accounting_method, defer_invoice_booking, entity_type, invoice_payment_accounts, bank_name, clearing_number, account_number, bankgiro, plusgiro, swish, iban, bic, vat_registered, vat_number')
     .eq('company_id', companyId)
     .single()
 
@@ -2726,6 +2736,15 @@ async function commitMarkInvoiceSent(
     }
   }
 
+  if (!hasRequiredSellerVatNumber(settings as CompanySettings, invoice as Invoice)) {
+    return {
+      error:
+        getErrorEntry('INVOICE_SEND_VAT_NUMBER_MISSING')?.message_sv
+        ?? 'Momsregistreringsnummer saknas i företagsinställningarna.',
+      status: 400,
+    }
+  }
+
   try {
     await ensureInvoiceNumber(supabase, companyId, invoice as Invoice)
   } catch (err) {