Display estimated bridge time and fee before confirming CrossChainPayment

[Kingsman-99]

Description

CrossChainPayment initiates cross-chain bridge transactions without showing the user how long bridging will take or what fees will be charged. Displaying an estimated bridge time (e.g. "~3 minutes") and a bridge fee estimate before the user confirms reduces surprises and failed transactions.

Acceptance Criteria

• After the user selects a source chain and amount, an estimate panel shows bridge time and total fee
• The estimate refreshes when the amount or chain changes
• A loading skeleton is shown while the estimate is fetching
• If no estimate is available a "Estimate unavailable" message is shown, not a blank area
• Existing tests continue to pass

Context

• Target file: src/components/CrossChainPayment.tsx