feat: payment matching audit trail and partial payments (#89)

* feat: payment matching audit trail, partial payments, and match improvements

- Add payment_match_log table (append-only audit trail per BFL 7:1) with
  immutability triggers and proper RLS
- Add invoice_payments table for partial payment tracking, mirroring
  supplier_invoice_payments pattern
- Add remaining_amount column + partially_paid status to invoices
- Add match-log.ts service for recording match/unmatch state transitions
- Improve match-invoice route: support partial payments, record audit log,
  emit payment.matched events, handle storno conflicts
- Improve match-supplier-invoice route: audit logging, partial payment support
- Update invoice-entries.ts for partial payment journal entries
- Update transaction ingest to detect and auto-suggest invoice matches
- Update bank-reconciliation to handle partial payment state
- Add invoice_payments, payment_match_log types and helpers
- Extend tests for match-invoice route and transaction ingest

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: address review feedback — payment matching correctness bugs

- P1: Return 500 on non-23505 payment insert failures instead of
  silently continuing with corrupted invoice state (both routes)
- P1: Fix foreign-currency partial payment matching — use proportional
  remaining SEK amount instead of full total_sek
- P2: Check error when clearing journal_entry_id after storno
- P2: Add updated_at column + trigger to invoice_payments table
- P2: Make supplier_invoice_payments.user_id NOT NULL after backfill

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/helpers.ts

@@ -11,6 +11,7 @@ import type {
   DocumentAttachment,
   TaxCode,
   Invoice,
+  InvoicePayment,
   Customer,
   Supplier,
   SupplierInvoice,
@@ -309,12 +310,33 @@ export function makeInvoice(overrides: Partial<Invoice> = {}): Invoice {
     converted_from_id: null,
     paid_at: null,
     paid_amount: null,
+    remaining_amount: 12500,
     created_at: '2024-06-15T14:30:00Z',
     updated_at: '2024-06-15T14:30:00Z',
     ...overrides,
   }
 }
 
+export function makeInvoicePayment(
+  overrides: Partial<InvoicePayment> = {}
+): InvoicePayment {
+  return {
+    id: nextId(),
+    user_id: 'user-1',
+    invoice_id: 'invoice-1',
+    payment_date: '2024-07-01',
+    amount: 12500,
+    currency: 'SEK',
+    exchange_rate: null,
+    exchange_rate_difference: 0,
+    journal_entry_id: null,
+    transaction_id: null,
+    notes: null,
+    created_at: '2024-07-01T00:00:00Z',
+    ...overrides,
+  }
+}
+
 export function makeCustomer(overrides: Partial<Customer> = {}): Customer {
   return {
     id: nextId(),