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>

types/index.ts

@@ -32,7 +32,7 @@ export type CustomerType =
   | 'non_eu_business'   // Non-EU company
 
 // Invoice status
-export type InvoiceStatus = 'draft' | 'sent' | 'paid' | 'overdue' | 'cancelled' | 'credited'
+export type InvoiceStatus = 'draft' | 'sent' | 'paid' | 'partially_paid' | 'overdue' | 'cancelled' | 'credited'
 
 // Invoice document type
 export type InvoiceDocumentType = 'invoice' | 'proforma' | 'delivery_note'
@@ -438,6 +438,25 @@ export interface SupplierInvoicePayment {
   created_at: string
 }
 
+// Invoice Payment (partial payments)
+export interface InvoicePayment {
+  id: string
+  user_id: string
+  invoice_id: string
+
+  payment_date: string
+  amount: number
+  currency: string
+  exchange_rate: number | null
+  exchange_rate_difference: number
+
+  journal_entry_id: string | null
+  transaction_id: string | null
+  notes: string | null
+
+  created_at: string
+}
+
 // Invoice
 export interface Invoice {
   id: string
@@ -498,6 +517,7 @@ export interface Invoice {
   // Payment tracking
   paid_at: string | null
   paid_amount: number | null
+  remaining_amount: number
 
   created_at: string
   updated_at: string
@@ -505,6 +525,7 @@ export interface Invoice {
   // Relations (populated when fetched)
   customer?: Customer
   items?: InvoiceItem[]
+  payments?: InvoicePayment[]
 }
 
 // Invoice Item