docs: ship in-house RN checkout, scope 5 follow-up tasks (#7-11)

In-house Request Network checkout went fully end-to-end on dev today.
A real 0.01 USDC payment flowed through wallet connect -> approve ->
ERC20FeeProxy.transferFromWithReferenceAndFee -> RN webhook ->
TransactionSafetyProvider -> Payment.status=completed -> page success
state. Tx 0x494c77a29161b5100d8e0b1ac675f1822955d0bb3633ecdbfafb886f84f2f320.

Docs:
- New PRD: Wallet, Multichain, Confirmations, AML, Trezor
  (5 follow-ups, each sized for an independent contributor)
- Updated PRD: Request Network In-House Checkout (phases 0..3 done,
  phase 4 partial, phases 5-6 not started)
- Updated handoff: deployed versions, what is working end-to-end,
  follow-up tasks index

Taskmaster: 5 new top-level tasks (#7..#11) covering ephemeral
destination wallets, multichain proxy registry + USDC/USDT, runtime
confirmation thresholds, optional seller-paid AML screening, and
Trezor signing for admin actions. Tasks are scoped fine-grained so
each is independent enough for kimi to pick up.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

08 - Operations/Monitoring.md

@@ -181,6 +181,8 @@ Today these are read manually from logs / Sentry. As Prometheus is added, encode
 |--------|-------|---------|-------|
 | Payment success rate | `db.payments.aggregate([{$group:{_id:"$status",n:{$sum:1}}}])` | > 95 % completed of 24h-old payments | < 90 % |
 | Webhook signature failures | log `Webhook verification failed` | 0 | > 0 |
+| Request Network webhook 4xx | nginx access log `/api/payment/request-network/webhook` | 0 | any real provider delivery returning 4xx |
+| Request Network safety-pending payments | `db.payments.find({"metadata.transactionSafety.status":"pending"})` | explained/short-lived | pending > 10 min without operator note |
 | SHKeeper API errors (5xx) | log + Sentry | 0 | > 5/min sustained |
 | Payouts stuck in `pending` > 30 min | `db.payments.find({type:'payout',status:'pending',createdAt:{$lt:ISODate(30 min ago)}})` | empty | non-empty |
 | Missing `transactionHash` after `completed` | the same query that drives `fix-transaction-hashes.js` | empty | non-empty |