`swarmctl login --swarm X` failed with "unexpected argument", and
`login --help` listed no `--swarm`: the flag was only accepted before the
verb. `--swarm` and `--ca-file` are now global, so they parse on either side
of the subcommand and show in every subcommand's help.
`--swarm` / `SWARMCTL_SWARM` accept a bare domain and prepend `https://`.
A value with a scheme is parsed as before, so `http://` is still refused.
On a swarm-controller host, the swarmctl wrapper sets
`SWARMCTL_LOGIN_DEFAULT_SWARM=https://<swarm.domain>` (`--set-default`).
Only `login` reads it, after `--swarm` and `SWARMCTL_SWARM`. The wrapper
does not set `SWARMCTL_SWARM`: that would send every socket verb (agent
create, schedule, inference, forge) through the gateway and make each need
a login. Other verbs resolve exactly as before.
No CA file is wired. The only CA material the module names is the
controller's assembled trust bundle (system CAs plus the hive anchor).
`--ca-file` hands every certificate in it to rustls-platform-verifier as
an extra root, and that fails the whole client on any one it cannot
parse, so pointing it at the system CAs is a risk nothing here can test.
The controller daemon trusts the same CA through `SSL_CERT_FILE`, which
skips unparsable certificates; using that for swarmctl is left open.
Machines that are not swarm-controller hosts (an operator laptop) get no
default; that case waits on an answer in the issue.
Fixes#5239