slab-menubar: tailnet peer submenu with click-to-ssh
Adds a "Tailnet: N/M online" submenu populated from `tailscale status
--json`, sorted online-first. Clicking a peer opens Terminal.app and
runs `ssh <hostname>`. Gracefully degrades if tailscale isn't installed
or responding.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>