Replaces the raw IllegalArgumentException thrown by GalaxyBrowseCommand for
--depth < 0 with a CommandLine.ParameterException so picocli surfaces a clean
single-line error instead of an unhandled stack trace. Adds an upper bound of
50 (matching the Python client) so --depth > 50 is also rejected cleanly.
Emits a stderr warning when --parent 0 is supplied explicitly, matching
Go/Rust client behaviour, because gobject id 0 is the server's root-walk
sentinel and passing it via --parent is almost always a mistake.
Adds three new tests: negative depth, depth > 50, and the --parent 0 warning path.
Joseph Doherty
b298ca74be