fix: make mobile navigation toggle keyboard accessible

[musshiyaki]

Summary

Make the mobile navigation menu toggle a native button so it can be reached and activated with keyboard navigation.

This also adds aria-expanded/aria-controls to expose the menu state and updates the existing mobile menu E2E coverage to verify Enter and Space activation.

Fixes: #7895

Validation

• pnpm exec prettier packages/ui-components/src/Containers/NavBar/index.tsx packages/ui-components/src/Containers/NavBar/index.module.css apps/site/tests/e2e/general-behavior.spec.ts --check
• pnpm --filter @node-core/ui-components lint
• pnpm --filter @node-core/ui-components lint:types
• pnpm --filter @node-core/website lint:js
• pnpm --filter @node-core/website lint:types
• PLAYWRIGHT_BASE_URL=http://localhost:3000 pnpm --filter @node-core/website playwright tests/e2e/general-behavior.spec.ts -g "functioning mobile menu" --project=chromium
• git diff --check

Note: local validation was run with Node.js v25.8.2, so apps/site emitted its expected node: 24.x engine warning, but the checks above completed successfully.

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Project	Deployment	Actions	Updated (UTC)
nodejs-org	Ready	Preview	May 31, 2026 4:35pm

[cursor]

PR Summary

Low Risk
Localized NavBar accessibility and presentation change with added E2E coverage; no auth, data, or API impact.

Overview
Replaces the mobile nav checkbox + label pattern with a native button that toggles menu visibility via React state, so keyboard users can focus and activate it with Enter and Space.

The collapsible panel gets a stable id="navbar-menu", wired with aria-controls and aria-expanded. Visibility is driven by isMenuOpen (flex vs hidden, with xl:flex unchanged on desktop) instead of CSS peer-checked. Toggle styling adds focus-visible ring treatment and drops the hidden checkbox markup.

E2E coverage targets #navbar-menu and asserts keyboard open/close after the existing click toggles.

^{Reviewed by Cursor Bugbot for commit 1e8e264. Bugbot is set up for automated code reviews on this repo. Configure here.}