[client] Add keyboard shortcut (Escape) to close mobile nav menu

[Otaiki1]

Summary

The mobile navigation menu in Navbar.tsx can be opened by a button press but likely does not close when the user presses Escape, violating WCAG 2.1 criterion 2.1.2 (No Keyboard Trap).

What to do

1. Add a useEffect in Navbar.tsx that listens for keydown with key === 'Escape' and closes the mobile menu.
2. Return focus to the hamburger toggle button when the menu closes.
3. Add an overlay/backdrop behind the mobile menu that also closes it on click.
4. Test with Playwright that pressing Escape dismisses the menu.

Acceptance criteria

• Pressing Escape closes the mobile nav.
• Focus returns to the trigger button after close.
• The test in Navbar.spec.tsx covers the Escape key path.

[habnark]

@habnark has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello can i work on this issue

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

[Macnelson9]

@Macnelson9 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi team, I'd like to take on this issue.

I specialize in Rust development, smart contract engineering, and frontend development with Next.js, React, and TypeScript. My experience allows me to bridge on-chain functionality with intuitive user experiences, ensuring both technical correctness and usability.

I'll follow the existing codebase conventions, communicate progress clearly, and deliver a high-quality solution within the expected timeline.

Thank you for your consideration.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Macnelson9 to this issue.

[drips-wave]

Congratulations, @habnark! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @habnark: 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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