* Guard plugin-add against git transport-helper URLs
omarchy-plugin-add cloned a user-supplied git URL without the
transport-helper guard that omarchy-theme-install already applies
(added in #7884, which did not touch plugin-add). Port that guard
(reject ext::/fd:: and leading-dash forms, keep https/ssh/scp-style
incl. IPv6) and add a regression test. Stock systems are unaffected
(git default protocol.ext.allow=never); this removes the silent
dependency on that default and aligns the two install paths.
* Test the plugin-add guard's leading-dash arm via the gum input path
The prior leading-dash cases only exercised the argv option parser, not
the guard (removing the guard's -* arm left them green). Drive a dash
value through the interactive gum prompt under a pty so the post-input
guard is actually covered; skip cleanly where util-linux script is
unavailable.
