feat: add lobby-to-room thin slice for issue #1

[phanlehieu10]

/claim #1

Summary

• add a basic lobby form for display name + room name
• redirect users into a shareable room URL
• render room metadata and invite URL on the room page
• add tests for the lobby -> room flow
• document current scope and next recommended steps in README

Why this is only a thin slice

The issue asks for a multi-user video call website using Algora tokens, but the repo currently has no token issuance, no WebRTC/media implementation, no presence layer, and no dependencies/setup docs. This PR intentionally stops at a truthful first slice instead of faking a complete video-call feature.

Test plan

• create a fresh venv
• install Django 4.x
• run python manage.py test

Follow-up work

• add a backend endpoint for Algora-compatible token issuance
• implement real room presence / membership state
• connect static/js/stream.js to actual media/session logic
• replace the placeholder tile with real WebRTC client behavior