Clipboard helper for macOS, Linux and Windows. Two modes — (a) proactive: when your next response includes text the user will need to paste somewhere external (a query for Grafana, a shell command, a config snippet, JavaScript for the browser console), show it inline as usual AND ask via AskUserQuestion if they want it copied to clipboard; (b) user-invoked: when the user types `/clipboard:copy [optional target]`, skip the confirmation and copy immediately (best-effort selection from the previous response, or the target the user named).
