feat: add self-contained legacy timer viewer for old browsers

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

apps/server/src/setup/index.ts

@@ -95,6 +95,8 @@ export const srcFiles = {
   translationReadme: join(srcDir.root, config.user, config.translations.directory, 'README.md'),
   /** Path to login */
   login: join(srcDir.root, 'html/login.html'),
+  /** Path to legacy timer for old browsers */
+  timerLegacy: join(srcDir.root, 'html/timer-legacy.html'),
   /** Path to ontime-logo */
   logo: join(srcDir.root, config.user, config.logo, 'ontime-logo.png'),
 };