Bug/customer invoice bug (#628)

* fix(supplier-invoices): self-assess reverse-charge VAT + link payments to vouchers

Reverse-charge supplier invoices now carry a per-item reverse_charge_rate (0.06/0.12/0.25). Under omvänd skattskyldighet the supplier charges 0% VAT, so the line vat_rate stays 0 and the buyer self-assesses fiktiv moms at the statutory rate. Centralizes rate resolution (resolveReverseChargeRate) and the ruta 20-24 basis-account guard (isReverseChargeBasisAccount) in vat-entries so the booking engine and review-dialog preview can no longer drift.

Adds the link_supplier_invoice_voucher pending operation: mark a leverantorsfaktura paid by linking an existing posted verifikat that debits 2440, with no new journal entry. Exposes find-candidates/link MCP tools and the bulk-reconcile helper, scoped under suppliers:read/write.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(vat): report yearly VAT over the rakenskapsar, not the calendar year

Annual VAT (helarsmoms) is filed per beskattningsar/rakenskapsar (SFL 26 kap), which can be extended or shortened up to 18 months. The previous Jan-Dec calendar span silently dropped part of an extended first year. calculateVatDeclaration now accepts a fiscalPeriodId and resolves the period's actual bounds for yearly; monthly/quarterly stay calendar. The reports UI passes the selected fiscal period, defaults the periodicity from the company's moms_period setting, and carries the period into the ruta drill-down. full-archive export threads the period id through too.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(migration): resolve supplier invoice status from payment amounts

The provider's lifecycle status and its payment status are computed independently upstream and can contradict each other (e.g. a Fortnox invoice marked booked but fully paid). Both the arcim entity-mapper and the Fortnox mapper now let payment state win: fully paid -> paid, partial -> partially_paid, otherwise the mapped lifecycle status, with credit notes forced terminal. Balance is compared numerically (never strict === 0) so float drift or a residual ore resolves cleanly, and an absent Balance is treated as unpaid.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(enable-banking): only ingest booked transactions to stop re-import drift

Pending entries are skipped during sync: a pending row is unstable across syncs (a later 'synka nu' returns it still pending or finally booked, often with a different effective date). Because both the dedup external_id and the content-dedup key are date-derived, that drift minted a new id and re-imported a transaction that already existed - observed in production as the same amount+description landing twice with different dates. Gating the import set on a stable booking_date removes the drift at the source and leaves booked rows' ids byte-identical.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* chore(gitignore): ignore local SIE test fixtures

tests/fixtures/sie/ may contain real or scrubbed company data and must never be committed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fix(invoice): handle errors during registration journal entry creation and ensure invoice rollback
feat(tests): add test for reverse charge rate handling on supplier invoice line items
feat(fortnox): ensure paid status reflects zero balance for fully paid invoices
chore(migrations): add reverse_charge_rate to supplier_invoice_items and backfill link_supplier_invoice_voucher

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Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/api/schemas.ts

@@ -355,6 +355,16 @@ export const CreateSupplierInvoiceItemSchema = z.object({
   // currency rounding, or POS receipts where supplier-side rounding makes the
   // VAT off by öre.
   vat_amount: z.number().min(0).optional(),
+  // Self-assessed VAT rate for omvänd skattskyldighet (reverse charge). The
+  // supplier charges no VAT (vat_rate stays 0); this is the Swedish statutory
+  // rate the buyer self-assesses at — 25% huvudregel default, 12%/6% for
+  // reduced-rated services (ML 6 kap 34 §). Must be a statutory rate.
+  reverse_charge_rate: z
+    .number()
+    .refine((r) => r === 0.06 || r === 0.12 || r === 0.25, {
+      message: 'reverse_charge_rate must be 0.06, 0.12, or 0.25',
+    })
+    .optional(),
   vat_code: z.string().optional(),
   quantity: z.number().optional(),
   unit: z.string().optional(),