Per-Merchant Collection Limits

Enforced in api/fees.ts → checkMerchantLimits():

Limit	Default	Enforcement
Per operation	10 USDC	In-memory check
Daily	500 USDC	SUM query on fee_ledger WHERE created_at >= today
Monthly	10,000 USDC	SUM query on fee_ledger WHERE created_at >= month_start

Exceeding a limit is non-blocking — the cheque works, the fee entry stays pending for manual review.