Simplify web push UX and updates

- Use a single endpoint
- Use a declarative web push sync hook. This thus handles all edge cases
  that had to be manually handled before: logout, login, account sync,
  etc.
- Simplify UX: browser notifications are always enabled (unless denied),
  web push toggle only shows up if permissions are already granted.

web/src/components/ActionBar.jsx

@@ -120,8 +120,6 @@ const ProfileIcon = () => {
 
   const handleLogout = async () => {
     try {
-      await subscriptionManager.unsubscribeAllWebPush();
-
       await accountApi.logout();
       await getDb().delete();
     } finally {