Add helper for displaying formatted transaction fee in buy confirmation

[Chucks1093]

Summary
The buy confirmation step shows a raw fee amount with no formatting context. A helper that formats the transaction fee with the correct unit and appropriate decimal precision makes the fee legible and consistent with other price displays in the UI.

Scope

• identify the transaction fee display in the buy confirmation step
• apply a formatting helper that includes the unit and correct decimal precision
• ensure the formatted fee is consistent with the key price display format

Acceptance Criteria

• the transaction fee is displayed with the correct unit and decimal precision
• the format matches the key price display convention
• the raw fee value is unchanged; only the display is formatted

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

[charlesbarleyman]

@charlesbarleyman has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, I’d like to work on this issue. I have experience building full-stack applications with Soroban, handling both smart contract logic and frontend integration, and I’m comfortable debugging and delivering clean, maintainable solutions. I focus on clear communication and incremental updates to ensure smooth collaboration. I can complete this task within 24–48 hours while maintaining code quality and proper testing. Looking forward to contributing!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @charlesbarleyman to this issue.

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Congratulations, @charlesbarleyman! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @charlesbarleyman: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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This issue has been completed by @charlesbarleyman as part of the Stellar Wave Program's 5th Wave 🥳

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