Link homepage virtual classroom to lobby auto-join and fix mobile layout

[Copilot]

Summary

This PR links the homepage Virtual Classroom CTA to the classroom page and auto-joins the lobby room. It also improves the classroom mobile layout so the canvas, controls, and chat are usable on narrow screens.

Changes

• Updated homepage Virtual Classroom CTA in /public/index.html to navigate to:
  • /classroom_poc.html?autojoin=1&room=lobby
• Updated CTA text to reflect behavior:
  • Join Lobby Classroom
• Added classroom entry parameter handling in /public/classroom_poc.html:
  • Auto-join when autojoin=1
  • Prefill room from room query parameter
  • Prefill display name from name query parameter or stored user profile
• Added sanitization for room and display-name inputs used by auto-join and join flow
• Refactored join flow into a reusable joinClassroom() function and used it for both manual and auto join
• Improved mobile responsiveness for classroom layout:
  • Main content switches to stacked layout on small screens
  • Chat panel becomes full-width with mobile-friendly height
  • Controls bar wraps more cleanly on small viewports

Validation

• pytest passes locally: 238 passed (existing warnings unchanged)
• parallel_validation run multiple times
  • CodeQL: no findings for analyzable languages in this change

Notes

• One recurring review suggestion requested adding role="button" to the homepage anchor CTA. This was not applied because it is a semantic navigation link (<a href=...>) and is already keyboard accessible by default.

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	learn	4d8c315	Apr 21 2026, 03:35 AM