Accounting: enforce accrual A/P on bill payments (match rule + guard + cleanup)

Under accrual, a vendor expense is recognized once — when the bill is entered
(Dr Expense / Cr A/P). Paying a bill must only relieve the liability
(Dr A/P / Cr Bank) and never re-hit the expense account. This hardens the
existing Pay Bills flow against re-recognition and double counting.

- Strict bill matching: extract a pure, dependency-free matcher into
  lib/billMatch.ts (debitMatchesBill/matchOpenBills) — same vendor, status
  open/overdue/partially_paid, amount within $0.01 of remaining (or <= remaining
  for partials), debit date within ±30 days of due/issue date. Unit-tested in
  billMatch.test.ts (covers the identical-recurring-charge regression).
- AccountingBankingPage.saveTx uses the strict rule (was "any open bill"), so a
  thrice-paid identical charge only clears the in-window bill.
- Bank-feed categorizer (bulkSetCategory) matches open bills before assigning an
  expense COA: single match clears A/P + links the bill; multi-match is skipped
  with a prompt to resolve in Pay Bills; no match categorizes as a direct expense.
- DB guard: add accounting.transactions.bill_id (FK -> bills) and CHECK
  chk_bill_payment_no_coa (bill_id IS NULL OR coa_account_id IS NULL) so a
  bill-linked payment can never carry an expense category. Both writers set
  bill_id on single-bill payments; partial payments now write partially_paid.
- One-time cleanup: clear coa_account_id on Ashley Manor's 8 double-counted bill
  payments ($2,198.98) so the GL reposts them as Dr A/P / Cr Bank.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

supabase/migrations/20260604120000_transactions_bill_link_and_ap_guard.sql

@@ -0,0 +1,22 @@
+-- Accrual A/P guard: link a bank transaction to the bill it settles, and enforce
+-- that a bill-linked payment never carries an expense category.
+--
+-- Under accrual, a vendor expense is recognized once — when the bill is entered
+-- (Dr Expense / Cr A/P). Paying the bill must only relieve the liability
+-- (Dr A/P / Cr Bank) via accounting.post_transaction_gl's vendor → A/P branch,
+-- which only runs when coa_account_id IS NULL. So any transaction that settles a
+-- bill must have coa_account_id NULL; otherwise it re-recognizes the expense.
+
+alter table accounting.transactions
+  add column if not exists bill_id uuid references accounting.bills(id) on delete set null;
+
+create index if not exists idx_transactions_bill_id
+  on accounting.transactions(bill_id) where bill_id is not null;
+
+-- Invariant: a transaction linked to a bill posts against Accounts Payable, never
+-- an expense account. This makes the accrual rule enforceable, not just convention.
+alter table accounting.transactions
+  drop constraint if exists chk_bill_payment_no_coa;
+alter table accounting.transactions
+  add constraint chk_bill_payment_no_coa
+  check (bill_id is null or coa_account_id is null);

supabase/migrations/20260604120500_cleanup_ashley_manor_double_counted_bill_payments.sql

@@ -0,0 +1,33 @@
+-- One-time remediation: Ashley Manor bill payments that double-counted the expense.
+--
+-- These bank debits settled an existing bill but were written with an expense
+-- coa_account_id, so the GL posted Dr Expense / Cr Bank — re-recognizing an expense
+-- already booked when the bill was entered, and never relieving Accounts Payable.
+-- Clearing coa_account_id makes accounting.post_transaction_gl repost them via the
+-- vendor → A/P branch as Dr A/P / Cr Bank, correcting prior periods. The matched
+-- bills are already marked paid, so paid_amount is intentionally left untouched.
+--
+-- Match rule (matches the accrual A/P matching rule used by the app): same vendor,
+-- bill not void/draft, amount within $0.01 of the bill total, debit date within
+-- ±30 days of the bill's due (else issue) date. When a single bill matches, the
+-- payment is linked via bill_id; ambiguous (multi-bill) matches clear coa only.
+with targets as (
+  select t.id as txn_id,
+    (select array_agg(b.id) from accounting.bills b
+      where b.company_id = t.company_id and b.vendor_id = t.vendor_id
+        and b.status <> 'void' and b.status <> 'draft'
+        and abs(b.total - t.amount) <= 0.01
+        and t.date between (coalesce(b.due_date, b.issue_date) - interval '30 days')
+                       and (coalesce(b.due_date, b.issue_date) + interval '30 days')
+    ) as bill_ids
+  from accounting.transactions t
+  join accounting.companies c on c.id = t.company_id
+  where c.name ilike 'Ashley Manor%'
+    and t.type = 'debit' and t.vendor_id is not null and t.coa_account_id is not null
+)
+update accounting.transactions t
+set coa_account_id = null,
+    bill_id = case when array_length(targets.bill_ids, 1) = 1 then targets.bill_ids[1] else null end
+from targets
+where t.id = targets.txn_id
+  and targets.bill_ids is not null;