Add helper for displaying network fee estimate before trade confirmation

[Chucks1093]

Summary
Users see the final network fee only after the transaction is built, which is too late to reconsider a trade based on fee cost. A pre-confirmation estimate helper that fetches and displays an approximate fee before the user confirms reduces surprise costs.

Scope

• add a helper that fetches a network fee estimate for the pending trade
• display the estimate in the trade flow before the confirmation step
• label the estimate clearly as approximate to set correct expectations

Acceptance Criteria

• a fee estimate is shown before the user reaches the confirmation step
• the estimate is labeled as approximate
• if the estimate fetch fails the UI shows a cannot estimate message rather than nothing

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg