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/Account.jsx

@@ -1078,8 +1078,6 @@ const DeleteAccountDialog = (props) => {
 
   const handleSubmit = async () => {
     try {
-      await subscriptionManager.unsubscribeAllWebPush();
-
       await accountApi.delete(password);
       await getDb().delete();
       console.debug(`[Account] Account deleted`);