feat(cash): mark how a transaction was paid, exclude cash from reconciliation

getPendingReconciliations treated every unreconciled manual transaction as
awaiting a matching statement row. Cash never appears on a statement, so a cash
entry sat in the queue indefinitely being offered matches within 3 days and 1%
on amount - and accepting one is silently destructive: reconciled manual rows
are filtered out of every query, so the cash spend disappears while the card
transaction it matched claims to be that same spend.

Migration 0016 adds transactions.payment_method (card | cash | bank_transfer |
other, NULL = unknown) with a CHECK constraint and a partial index. The notCash()
fragment excludes cash from both halves of the reconciliation query - the pending
list and the candidate match subquery, which aliases the manual row as m.

Only cash is excluded. Bank transfers do appear on a statement now that
transaction accounts are imported, and NULL means unknown, so both stay
candidates and every pre-existing row behaves exactly as before.

ATM withdrawals deliberately stay categorised as spend rather than transfers.
Treating them as transfers is only correct if every cash purchase is logged;
with partial logging it silently deletes the unlogged remainder from spend.

prisma/migrations/0016_payment_method/migration.sql

@@ -0,0 +1,35 @@
+-- How a transaction was paid for, so cash can be told apart from everything else.
+--
+-- The problem this solves: getPendingReconciliations treats every unreconciled
+-- manual transaction as awaiting a matching statement row. A cash purchase never
+-- appears on a statement, so it sits in the queue forever and is offered matches
+-- within 3 days and 1% on amount. Accepting one is silently destructive --
+-- reconciled manual rows are excluded from every query, so the cash spend
+-- disappears while the card transaction it matched claims to be that same spend.
+--
+-- NULL means unknown, which is treated as reconcilable -- the existing behaviour
+-- for every row already in the table.
+--
+-- Only 'cash' is excluded from reconciliation. A bank transfer DOES appear on a
+-- statement now that transaction accounts are being imported, so it stays a
+-- reconciliation candidate.
+
+ALTER TABLE transactions
+  ADD COLUMN IF NOT EXISTS payment_method TEXT;
+
+ALTER TABLE transactions DROP CONSTRAINT IF EXISTS transactions_payment_method_check;
+ALTER TABLE transactions ADD CONSTRAINT transactions_payment_method_check
+  CHECK (payment_method IS NULL
+         OR payment_method IN ('card', 'cash', 'bank_transfer', 'other'));
+
+-- Partial index: the reconciliation query filters on this, and cash is expected
+-- to stay a small minority of rows.
+CREATE INDEX IF NOT EXISTS idx_transactions_payment_method
+  ON transactions (payment_method) WHERE payment_method IS NOT NULL;
+
+-- Backfill the one row that is unambiguously cash. Statement-linked rows are
+-- left NULL: they came from a statement, so by definition they are not cash.
+UPDATE transactions
+SET payment_method = 'cash'
+WHERE statement_id IS NULL
+  AND description ILIKE '%cash transaction%';

prisma/schema.prisma

@@ -175,6 +175,7 @@ model transactions {
   row_index               Int?
   merchant_normalized     String?
   amount_aud              Decimal?      @db.Decimal(12, 2)
+  payment_method          String?       // card | cash | bank_transfer | other; NULL = unknown (migration 0016)
   owner_id                Int?
   reconciled_with_id      Int?
   principal_amount        Decimal?      @db.Decimal(12, 2)