set-args interprets --help as a value instead of showing help

[edimuj]

claude-rig set-args --help stores --help as the global default args instead of showing help for the set-args command.

This causes every subsequent claude-rig launch (and bare claude-rig auto-launch) to forward --help to Claude, which then prints its help text and exits instead of starting a session.

Repro:

claude-rig set-args --help
claude-rig launch minimal   # prints Claude help and exits

Expected: set-args --help should show usage info for the set-args subcommand.

Workaround: Clear the file manually: echo -n "" > ~/.claude-rig/default-args