Add app version management, update checks, and periodic SW updates

- Introduced version.json and appVersionAssetPlugin for build-time version tracking.
- Enhanced settings page with update check/status UI.
- Refactored bootstrap to handle SW updates and initiate periodic checks.

README.md

@@ -93,6 +93,7 @@ For installability and service worker support:
 
 - serve `manifest.webmanifest` with an appropriate web manifest content type
 - make sure `service-worker.js` is reachable from the deployed site root
+- make sure `version.json` is reachable from the deployed site root for app update checks
 - avoid aggressive caching on `index.html` during upgrades so new builds are picked up reliably
 
 ### Smoke test after deployment
@@ -113,6 +114,7 @@ public/
   manifest.webmanifest
   offline.html
   service-worker.js
+  version.json
 src/
   api/
   app/