Migration from the retired USDC protocol

This is a breaking replacement, not an on-chain upgrade. Existing v1 objects remain on Sui but the repository no longer builds clients or interfaces for them. Applications that still need historical v1 behavior must pin their old code and treat it as unsupported.

Retired surface	Current replacement
USDC-only amount helpers	Coin base-unit bigint plus CoinMetadata display
AdminConfig currency/fee policy	AssetRegistry allowlist; protocol fee is 0
Direct payment creation	Merchant Product → merchant-created Order → exact Coin payment
No on-chain refund	Bounded Payment<T> escrow and payer-requested refund
Old payment/merchant/admin SDK modules	assets, merchants, catalog, orders, payments, subscriptions
v1 package/object environment IDs	Fresh packageId and assetRegistryId from a future approved deployment

Do not reuse the retired Package, AdminConfig, or capability IDs. There is no state migration script and no compatibility shim.