Implements ZMQ command protocol for dashboard-to-agent communication:
- Agents listen on port 6131 for REQ/REP commands
- Dashboard sends "refresh" command when 'r' key is pressed
- Agents force immediate collection of all metrics via force_refresh_all()
- Fresh data is broadcast immediately to dashboard
- Updated help text to show "r: Refresh all metrics"
Also includes metric-level caching architecture foundation for future
granular control over individual metric update frequencies.
Christoffer Martinsson
6bc7f97375