v1.2.1 - waycentral

Event-driven lock keys, aligned clock

- Lock keys: keep the keyboards open and poll() them for lock key / LED
  events instead of reopening /dev/input every second; output changes
  immediately (new wc_lock_monitor_* API)
- Clock ticks on the second boundary and date on the minute boundary
  instead of drifting with sleep()
- Bump version to 1.2.1

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>