Brummel
e4eb70f083
`aura --help` and `aura -h` are a newcomer's reflex first command but
fell through to the catch-all unknown-subcommand arm: exit 2, empty
stdout, error text on stderr. The conventional help affordance returning
the error path is a C22 first-contact friction (milestone fieldtest).
Add a `Some("--help") | Some("-h")` arm before the catch-all that prints
the usage to stdout and returns normally (exit 0). The `_ =>` error path
is untouched, so an unknown subcommand still prints `aura: usage: aura
run` to stderr and exits 2 -- pinned by the negative-preservation
assertion in the RED test (07ba20a). Verified: cli_run.rs all green
(help/no-args/run), clippy --all-targets -D warnings clean.
Minimal slice per the tdd handoff: the stdout help literal ("usage: aura
run") and the stderr error literal ("aura: usage: aura run") are left as
two distinct user-facing strings rather than factored into a shared
usage constant -- a single usage source is a deliberate non-goal here,
left for a future cycle if one wants it.
closes #20