Expired access tokens require manual intervention (e.g. "soft_logout")

With session saving in play, after this happens:
```plain
error in process sentinel: ement-api-error: Ement API error: "401: Access token has expired"
error in process sentinel: Ement API error: "401: Access token has expired"
```
It appears to be necessary to (after disconnecting) manually edit the saved session file and remove the invalid entry before attempting to reconnect.

Without doing that, running `ement-disconnect` and then `ement-connect` results in a HTTP 401 error due to the invalid token, and it does not attempt to reauthenticate and nor does it purge the invalid session from the file, so trying again will simply produce the same result:

> Ement: Sync request sent, waiting for response...
error in process sentinel: Ement API error: "Ement: Unrecognized network error", #s(plz-error nil #s(plz-response 2 401 ((server . "nginx") (date . "Wed, 21 Jun 2023 11:31:39 GMT") (content-type . "application/json") (cache-control . "no-cache, no-store, must-revalidate") (access-control-allow-origin . "*") (access-control-allow-methods . "GET, HEAD, POST, PUT, DELETE, OPTIONS") (access-control-allow-headers . "X-Requested-With, Content-Type, Authorization, Date") (strict-transport-security . "max-age=63072000")) "{\"errcode\":\"M_UNKNOWN_TOKEN\",\"error\":\"Access token has expired\",\"soft_logout\":true}") nil) [2 times]