fleet: serve <role> --help (and queue-broker --help / secrets-broker --help) starts the daemon instead of printing help

Evidence (verified this run, laptop primary @ eb3e71c)

pkgs/fleet/crates/fleet/src/main.rs, run_domain: the domain-help shortcut only inspects args.first():

if matches!(args.first().map(|s| s.as_str()), Some("--help") | Some("-h") | Some("help")) {
    print_domain_help(surface, d);
    return EXIT_OK;
}

For the serve domain the first argument is the role, so a help flag in position 2 is never seen. The call falls through to the broker entry points — fleet_queue::queue_broker::run() and fleet_queue::secrets_broker::run() (pkgs/fleet/crates/fleet-queue/src/queue_broker.rs:589, secrets_broker.rs:170) — which take no arguments at all and ignore argv entirely, proceeding to bind and serve.

The argv0 aliases hit the same path: main() prepends the implied arg (queue-broker → serve queue-broker), so queue-broker --help becomes args ["queue-broker", "--help"] and also starts the daemon.

Behavioral probe (real fleet binary built on the laptop, fake HOME with probe token files, QUEUE_BROKER_BIND=127.0.0.1:0, 3s timeout):

$ fleet serve queue-broker --help
queue-broker: listening on 127.0.0.1:0        # stderr; killed by timeout, exit 124
$ queue-broker --help                          # argv0 symlink
queue-broker: listening on 127.0.0.1:0        # stderr; killed by timeout, exit 124
$ fleet serve --help                           # control
fleet serve — Run a fleet daemon role …        # domain help, exit 0

Why it matters

--help is the safe, reflexive first command for any operator or agent meeting a new daemon binary. Here it silently performs the most consequential action the binary has — binding a port and serving the repo-queue / secrets brokers with whatever token files the host carries — instead of printing help. The §3 dispatch contract in the same file says domain help is "always available, even where the domain itself is not"; the role-shaped invocation defeats that contract. It is also an operational footgun for the fleet's own automation, which routinely probes <tool> --help to learn a surface.

Acceptance criteria

• fleet serve queue-broker --help, fleet serve secrets-broker --help (and -h / help in the same position) print the serve domain help and exit 0, without binding anything.
• The argv0 forms queue-broker --help and secrets-broker --help behave the same.
• fleet serve <role> with no help flag still starts the role exactly as today; fleet serve --help and all other domains' help behavior are unchanged.
• A test pins the help-after-role routing (e.g. at the dispatch level) so the implied-arg alias route cannot regress it.