Backend:
- POST /api/matches/confirm — atomic payment creation + transaction match
- POST /api/matches/:transactionId/unmatch — soft-delete payment, reset transaction
- Account transactions include matched_bill_id and matched_bill_name
Frontend:
- Unmatched transactions show + match pill button
- BillPickerDialog with transaction details + searchable bill list
- Confirm creates payment and updates row immediately
- Matched transactions show Unlink icon to remove match
- Toast on success with bill name and date
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