Without it, WezTerm tries to run its own mux protocol over the SSH
session (spawning `wezterm cli --prefer-mux proxy` on the remote),
which fails with "Please install the same version of wezterm on both
the client and server" whenever the remote host doesn't have wezterm
installed -- the case for a plain SSH target. multiplexing = "None"
makes the domain behave like a normal SSH terminal instead.
update_ssh_domain's match pattern is now a lazy "match to the next
closing brace" instead of assuming an exact 3-field shape, so it can
still find and replace entries saved before this change (without the
multiplexing field) as well as ones saved after.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>