Xchain Bridge Send

Build the swapAndBridge calldata server-side and return it for MetaMask to sign.

Body schema: Required: evm_address, chain_id, usdc_address, bridge_amount One of: algo_address (legacy field name, used for Algorand destination) recipient_address (preferred — works for any destination)

Returns: { to, data, value } — pass directly to eth_sendTransaction.

The destination chain is taken from the tenant's xchain_destination_chain setting; the frontend doesn't pass it (and shouldn't be allowed to, because that would let a hostile shopper redirect bridge inflow to a different chain).