Bug/momsdek overflow (#465)

* feat(settings): add option for company name position in invoice PDF

* feat(migrations): add backfill for VAT account labels to correct bad seed data

* feat(migrations): add backfill for VAT account labels to correct bad seed data

* fix(ui): improve accessibility for company name position toggle in PDF settings

* fix(bookkeeping): align BAS 2026 reference data with official PDF

Reconciled lib/bookkeeping/bas-data/ against the BAS 2026 v1.1 official
chart (1286 accounts). All real discrepancies fixed:

- 2089 Fond för utvecklingsutgifter: k2_excluded → true
- 8417 Räntekostnader för dold räntekompensation: k2_excluded → true
- 1250, 1260 renamed to "(Fritt konto för Inventarier, verktyg och
  installationer)" — BAS 2026 freed these slots
- Periodiseringsfond 2120-2139: added year suffixes (2120 = "...2020"
  etc.) and added 8 missing accounts (2121-2127, 2129) for years
  2019, 2021-2027. Dropped phantom 2022/2024 prior-parser garbage.
- 4075-4078: EUland → EU-land
- 8411: förlagsoch → förlags- och

Verified: 1282 of 1286 PDF accounts match exactly after edits (remaining
4 are PDF-parser artifacts, not real data). Build clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(migrations): backfill BAS 2026 account labels in chart_of_accounts

Companion to the TS reference fix. Updates existing companies' rows where
they still carry seed-data typos or generic names that don't match BAS 2026:

- 4075-4078: EUland → EU-land (hyphenation)
- 8411: förlagsoch → förlags- och (hyphenation)
- 2120, 2130-2137, 2139: rename "Periodiseringsfond" (generic, no year) to
  the BAS 2026 canonical name with year suffix

Defensive: every WHERE clause matches an EXACT current value. Rows that
have been manually renamed by users — including those with a wrong year
that may reference legacy fonds from an earlier BAS numbering cycle — are
left untouched. No row is deleted.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(migrations): fix wrong-year labels on Periodiseringsfond accounts

Follow-up to 20260513140000. The first backfill only renamed accounts whose
name was the generic "Periodiseringsfond" (no year). Many customers were
seeded from an older BAS numbering cycle where 2126 = "2016", 2127 = "2017",
etc. — BAS 2026 reuses those account numbers for years 2026/2027.

This migration aligns the year tag with the BAS 2026 meaning of each
account number across 2120-2127, 2129, 2130-2137, 2139. Only rows whose
name still starts with "Periodiseringsfond" are touched — customers who
renamed the account to something custom keep their name.

Verified on staging: all 18 accounts now carry BAS 2026 canonical names.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(data): update account names and descriptions for clarity and consistency

* fix(migrations): backfill account names for BAS 2026 freed accounts and refine Periodiseringsfond name matching

* feat: enhance VAT handling with reverse charge logic and supplier type support

* feat: implement VAT declaration validation rules and enhance moms box mapping

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/bookkeeping/mapping-engine.ts

@@ -2,6 +2,7 @@ import type { SupabaseClient } from '@supabase/supabase-js'
 import {
   generateInputVatLine,
   generateReverseChargeLines,
+  generateReverseChargeBasisLines,
 } from './vat-entries'
 import { findMatchingTemplates, buildMappingResultFromTemplate } from './booking-templates'
 import {
@@ -221,8 +222,13 @@ function buildResult(rule: MappingRule, transaction: Transaction, entityType?: E
   const vatLines: VatJournalLine[] = []
   if (isExpense && !rule.default_private && rule.vat_treatment) {
     if (rule.vat_treatment === 'reverse_charge') {
-      // EU reverse charge: fiktiv moms (offsetting entries)
-      const rcLines = generateReverseChargeLines(absAmount)
+      // Reverse charge: emit BOTH the fiktiv-moms pair (2645/2614) AND the
+      // basbelopp pair (44xx|45xx / 4598). The basbelopp pair populates
+      // momsdeklaration rutor 20–24; without it Skatteverket rejects with
+      // FK004. Mapping rules don't carry supplier-country today, so we
+      // default to EU services — the most common reverse-charge scenario.
+      const rcRate = 0.25
+      const rcLines = generateReverseChargeLines(absAmount, rcRate, false)
       for (const rcl of rcLines) {
         vatLines.push({
           account_number: rcl.account_number,
@@ -231,6 +237,19 @@ function buildResult(rule: MappingRule, transaction: Transaction, entityType?: E
           description: rcl.line_description || '',
         })
       }
+
+      // Skip basbelopp emission if the rule already books to a basis account.
+      if (!/^4[45]\d{2}$/.test(debitAccount)) {
+        const basisLines = generateReverseChargeBasisLines(absAmount, rcRate, 'eu_business')
+        for (const bl of basisLines) {
+          vatLines.push({
+            account_number: bl.account_number,
+            debit_amount: bl.debit_amount,
+            credit_amount: bl.credit_amount,
+            description: bl.line_description || '',
+          })
+        }
+      }
     } else if (rule.vat_treatment === 'standard_25' || rule.vat_treatment === 'reduced_12' || rule.vat_treatment === 'reduced_6') {
       const vatRate =
         rule.vat_treatment === 'standard_25' ? 0.25