feat: implement notifications

[dargmuesli]

Users should be able to receive notifications.

Web Push:

• https://blog.mozilla.org/services/2016/08/23/sending-vapid-identified-webpush-notifications-via-mozillas-push-service/
• https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/Tutorials/js13kGames/Re-engageable_Notifications_Push

Code inspiration:

• https://github.com/jeffposnick/yt-playlist-notifier/blob/main/src/service-worker/sw.ts
• https://vite-pwa-org.netlify.app/guide/development.html#injectmanifest-strategy
• https://github.com/elk-zone/elk/blob/main/service-worker/sw.ts
• https://github.com/elk-zone/elk/pull/337/files