ceph.in: reject -w/--watch flags when used with subcommands
parse_known_args() silently consumes -w and all --watch-* flags
before subcommand arguments reach the command validator. When a
user ran "ceph orch ps -w", the watch handler entered cluster log
streaming mode while discarding the subcommand entirely, with no
error or indication that the orch ps command was ignored.
Add a guard at the entry of the watch handler: if any watch flag
is active and childargs is non-empty, print "Invalid command:
unused arguments: [...]" and return EINVAL. This matches the
behaviour already seen when -s/--status is combined with a
subcommand.