Add validation for non-empty debit/credit accounts before creating journal
entries. Generate fiktiv moms lines (2645/2614) for EU reverse charge expenses.
Change default unmapped expense account from 6900 to 6991. Add tests for
reverse charge handling and exhaustive category mapping coverage.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add test coverage for invoices, transactions, bookkeeping, and supplier
invoice API routes. Includes test helpers (createMockRequest,
parseJsonResponse, createMockRouteParams, createQueuedMockSupabase) and
fixture factories (makeInvoice, makeCustomer, makeSupplier,
makeSupplierInvoice, makeCompanySettings).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>