Adds timer-legacy.html — a zero-dependency static page that connects
to the Ontime WebSocket and displays the live countdown for browsers
that cannot parse the Vite-built React bundle (Safari < 14, Chrome < 85).
Also adds a synchronous pre-React guard in index.html that redirects
/timer visitors to the legacy page when Promise.any is unavailable,
matching the Vite build target floor of Safari 14 / Chrome 85.
https://claude.ai/code/session_013MfdwdjdDUnr3akpGSGXa4
Claude