Payment status checks for notifications that never arrive

- src/payments/status.js: open checkouts, checkCheckouts and the
  payment-status job (every 15 min, checkouts 10 min - 3 days old). Found
  payments are settled exactly as their webhook would be (settlePayment,
  extracted from the webhook handler: amount check, record, emails).
- PayFast: signed API client (alphabetical signature, testing=true in
  sandbox), findPayments from the transaction history CSV matched on
  M Payment ID, and testConnection (signed /ping). Verified against a
  real sandbox account.
- Yoco documents no checkout lookup, so its checkouts are "can't check".
- Payments -> Reconcile: "Waiting for payment" with Check status /
  Check all; PayFast card: Test connection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/.env.example

@@ -69,6 +69,8 @@ CONSENT_JOBS_ENABLED=true
 # Waitlist: expire unclaimed offers and offer freed places (every 10 minutes by default)
 WAITLIST_JOB_ENABLED=true
 # WAITLIST_JOB_INTERVAL_MS=600000
+# Payments: every 15 minutes, look up PayFast checkouts whose notification never arrived
+PAYMENT_STATUS_JOB_ENABLED=true
 # Nightly database backup at 02:00 (requires the `pg_dump` binary on this host).
 # Retention count is set via Admin → Site Settings → Backups (default 14).
 BACKUP_ENABLED=true