Clickable slash-command links can include arguments and colour

Clickable slash-command links in Claude Code can now show arguments after the command, such as '/command args', and can be shown in a colour. Slash commands are commands you type starting with '/'. Before, a link showed only the command.

Separately, when a GitHub pull request request is refused with a sign-in error, Claude Code now reports that the sign-in failed. This does not apply when the error code starts with github_.