No operator path to withdraw settled payment funds (settle/withdraw commands removed) #37

Context

The payment settlement and withdraw functionality was removed in the Curio PDP core migration (#22, removal commit 195893a). Settlement itself is covered: Curio runs an automatic settlement task (curio/tasks/pay, adopted by Piri as part of the migration), so rails settle without operator action.

What's missing is withdrawal: once funds are settled to the operator's account in the payments contract, there is currently no way for an operator to move them out. Curio has no withdraw feature either — so this is a genuine gap for Piri operators, not a migration oversight of parity.

Open question

Where should withdraw live?

1. Not in Piri — Piri stays at parity with Curio; operators use external tooling. Cleanest, but today "external tooling" means hand-rolling a contract call.
2. A simple Piri command — pragmatic operator aid (piri client payment withdraw-style), packing withdrawTo and sending via the node's sender. Small surface, but adds a payments feature Curio itself doesn't carry.
3. https://pay.filecoin.cloud/ console support — the ideal home. Withdrawal is an account-holder action against the payments contract, not a storage-node function; the console serving it would make both Piri and Curio moot here.

Preference is (3); this issue tracks the gap until that exists, and is the place to decide whether (2) is warranted as a stopgap.

Old code (for a stopgap command)

At pre-migration commit 6bf7299:

• pkg/pdp/smartcontracts/payment.go — payments contract bindings incl. PackSettleRail / PackWithdrawTo
• pkg/admin/httpapi/handlers/payment.go — admin API handler with account/rail settlement math (incl. available-to-withdraw calculation)
• cmd/cli/client/admin/payment/ — the payment status CLI surface