hive-c0re logs in with the hive's matrix sender token and creates the
Space and rooms over swarm.matrix.apiUrl. On a hive that does not run
the homeserver that crosses the network, so the default is now
https://<gatewayHost>. hive-c0re already verifies against the hive trust
bundle (SSL_CERT_FILE: system CAs, swarm root and the store's services
root), which covers the gateway's leaf for that name.
Also drops the remaining loopback-default wording in hive-c0re's matrix
module and the openFirewall description, and pins the https default on a
hive host without the homeserver in module-eval-matrix-core.