feat(pwa): auto-update service worker so new releases take effect without manual cache clearing

- app.js: reload once on SW controllerchange (guarded against loops / first
  install) and poll reg.update() hourly for long-open tabs
- sw.js: bump cache to v24 so the new (network-first) worker replaces any stale
  cache-first worker and cleans old caches on activate

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v65';
+export const APP_VERSION = 'v66';