routing-manager.js read CFG_<APP>_HOST_NAME for its preview URL, but that
key was retired by the per-port subdomain refactor (2e4f420, 2026-05-22)
and no .config defines it anymore. The lookup always returned undefined,
so even with a configured domain the preview fell through to the
`<your-domain>` placeholder instead of showing the real host.
Now derives the preview from the port's own subdomain (parts[10] of
the 12-col PORT row), matching the canonical host_setup rule in
scripts/network/variables/variables_init_app.sh:
@ / root -> apex (`https://<domain>`)
set -> `https://<sub>.<domain>`
empty -> `https://<app>.<domain>`
Also adds `subdomain` to the port object emitted by _collectPorts so
this and any future per-row consumer can read it.
Signed-off-by: librelad <librelad@digitalangels.vip>
9d5d0103b6
