If a user logs out from a device the expectation should be that device
no longer having any association with the user's account. Any existing
push notifications should thefore be removed on server. For this reason
tie push notifications to a session, and remove them when the session is
deleted.
Provide a basic account system with login and server side session store
identified by a cookie. Upon successful login a signed session cookie
is set by the server with the session stored on the server identifying
which account it is logged in as. The client uses a shared useFetch on
the session endpoint to identify if it's logged in and which account it
is logged in as, and refreshes this when loggin in or out.
