Remove the custom htpasswdFile option and bind-mount. The htpasswd file
now lives at the fixed path /var/lib/hyperhive/gateway/gateway.htpasswd
on the host, which is already exposed inside the container at
/run/hive-state/gateway.htpasswd via the existing gateway state
bind-mount — no extra bind-mount needed.
A tmpfiles rule pre-creates the file so nginx can open it even before
any users exist (empty file → all requests return 401, which is correct).
hivectl gateway commands default --file to the standard path so
`hivectl gateway create-user alice` just works without any flags.