Drop the hardcoded-domain FQDN regex and every hardcoded domain from commons.
Node identity is now explicit in node.env: APEX_NODE_FQDN (real FQDN,
traefik Host()), APEX_NODE_HOST (public host name — backup --host,
obs/notify instance), APEX_SUBNET. The short name (log prefix, sync/<node>
branch, messages) is derived as the first host label.
notify instance is just the host (no hardcoded prefix); the git bot identity
moves to APEX_GIT_AUTHOR_NAME/EMAIL (node.env) with generic defaults. Alloy
node+instance labels use APEX_NODE_HOST. Fallbacks keep a node working if it
omits a var (host<-fqdn<-hostname).
BREAKING CHANGE: removes APEX_NODE and APEX_CLUSTER env vars; node name is now derived from APEX_NODE_FQDN
deytenit