feat: add foreign currency support, refactor bookkeeping engine, and improve invoice inbox document classification

- Add currency-utils module for SEK conversion with exchange rates
- Refactor createJournalEntry to use draft+commit flow preventing voucher number gaps (BFL 5 kap. 7§)
- Add foreign currency support to invoice entries with per-line SEK conversion
- Centralize category-to-account mapping into single source of truth
- Refactor invoice inbox to use shared document analyzer with document type classification (receipt, supplier invoice, government letter)
- Update mapping engine, supplier invoice entries, and transaction entries
- Fix report component rendering issues
- Add new validation schemas and tests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/core/bookkeeping/__tests__/storno-service.test.ts

@@ -29,6 +29,7 @@ function makeClient() {
 vi.mock('@/lib/bookkeeping/engine', () => ({
   validateBalance: vi.fn().mockReturnValue({ valid: true, totalDebit: 1000, totalCredit: 1000 }),
   getNextVoucherNumber: vi.fn(async () => ++resultIdx), // just increment
+  getSwedishLocalDate: vi.fn().mockReturnValue('2024-06-15'),
 }))
 
 import { correctEntry } from '../storno-service'

lib/core/bookkeeping/storno-service.ts

@@ -5,7 +5,7 @@ import type {
   JournalEntry,
   JournalEntryLine,
 } from '@/types'
-import { validateBalance, getNextVoucherNumber } from '@/lib/bookkeeping/engine'
+import { validateBalance, getNextVoucherNumber, getSwedishLocalDate } from '@/lib/bookkeeping/engine'
 
 /**
  * Storno Service - 3-step correction flow per Bokföringslagen
@@ -69,7 +69,7 @@ export async function correctEntry(
       fiscal_period_id: original.fiscal_period_id,
       voucher_number: reversalVoucherNumber,
       voucher_series: original.voucher_series || 'A',
-      entry_date: new Date().toISOString().split('T')[0],
+      entry_date: getSwedishLocalDate(),
       description: `Storno: ${original.description}`,
       source_type: 'storno',
       reverses_id: originalEntryId,
@@ -172,7 +172,7 @@ export async function correctEntry(
         fiscal_period_id: original.fiscal_period_id,
         voucher_number: correctedVoucherNumber,
         voucher_series: original.voucher_series || 'A',
-        entry_date: new Date().toISOString().split('T')[0],
+        entry_date: getSwedishLocalDate(),
         description: `Rättelse: ${original.description}`,
         source_type: 'correction',
         correction_of_id: originalEntryId,