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/app.ts

@@ -32,7 +32,7 @@ import { runtimeService } from './services/runtime-service/runtime.service.js';
 import { timerConfig } from './setup/config.js';
 import { environment, isProduction } from './setup/environment.js';
 // import utils
-import { publicDir, srcDir } from './setup/index.js';
+import { publicDir, srcDir, srcFiles } from './setup/index.js';
 import { populateDemo } from './setup/loadDemo.js';
 import { populateStyles } from './setup/loadStyles.js';
 import { populateTranslation } from './setup/loadTranslations.js';
@@ -113,6 +113,11 @@ app.use(`${prefix}/external`, (req, res) => {
 });
 app.use(`${prefix}/user`, express.static(publicDir.userDir, { etag: false, lastModified: true }));
 
+// Serve legacy timer for old browsers that don't support modern JS
+app.get(`${prefix}/timer-legacy`, authenticateAndRedirect, (_req, res) => {
+  res.sendFile(srcFiles.timerLegacy);
+});
+
 // Base route for static files
 app.use(`${prefix}`, authenticateAndRedirect, compressedStatic);
 app.use(`${prefix}/*splat`, authenticateAndRedirect, compressedStatic);