Add modal focus trap and escape handling for trade dialogs

[Chucks1093]

Summary
Add modal focus trap and escape handling for trade dialogs

Scope

• add keyboard focus trap for buy/sell modals\n- support escape key close behavior where safe\n- keep accessibility semantics intact

Acceptance Criteria

• scoped change is implemented with no unrelated file churn
• docs/tests are updated where applicable
• contributor can validate the outcome locally

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

[shoaib050326]

@shoaib050326 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Can you please assign this to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @shoaib050326 to this issue.

[Demilade01]

@Demilade01 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hey chucks, I will like to work on this!

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[floxxih]

@floxxih has applied to work on this issue as part of the Stellar Wave Program's 4th 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 @floxxih to this issue.

[drips-wave]

Congratulations, @floxxih! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @floxxih: 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.

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[drips-wave]

This issue has been completed by @floxxih as part of the Stellar Wave Program's 4th Wave 🥳

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