RI Marketplace: status poller (active->closed + proceeds/fee) + seller-account precondition UI (closes #292 remainder) #27

Context

PR LeanerCloud/cloud-commitments-cli#808 (closes LeanerCloud/cloud-commitments-cli#292) implements the AWS RI Marketplace list and cancel flows for Standard RIs. To keep that PR landable, two parts of LeanerCloud/cloud-commitments-cli#292 were intentionally descoped:

1. Status poller that transitions a listing active -> closed once it sells, and records realized proceeds and the AWS transaction fee actually charged.
2. Seller-account precondition UI that checks the AWS seller account is registered (US bank account on file) and surfaces a tailored message before the user attempts to list.

Because the poller is unimplemented, migration 000060 in PR LeanerCloud/cloud-commitments-cli#808 was reduced to only the three columns the implemented flow reads/writes (offering_class, listing_id, listing_state). The settlement/poller columns (listed_at, listing_price_schedule, listing_proceeds_received, listing_fee_paid) were removed so the schema never carries columns nothing populates. They should be re-added alongside the poller in this follow-up.

Scope

• Background poller (or on-demand refresh) calling DescribeReservedInstancesListings to update listing_state and detect closed (sold) listings.
• Persist realized proceeds and the AWS fee actually charged; re-add the settlement columns in a new migration.
• Seller-account precondition check + UI message (registered seller / US bank account on file) before listing.
• This completes the remaining requirements of feat(history): Sell-on-Marketplace button for Standard RIs (CreateReservedInstancesListing) with status polling + sell-{any,own} RBAC cloud-commitments-cli#292.

Out of scope

Listing creation and cancellation (already shipped in LeanerCloud/cloud-commitments-cli#808).