The monitor signal handlers (signal_monitor_added, signal_monitor_removed)
were never disconnected during SIGUSR2 reload. Each reload accumulated
additional handlers, causing multiple layer surfaces to be created when
monitors were hotplugged.
This fix:
- Stores signal connections as class members
- Disconnects them before reconnecting in bindInterfaces()
- Clears stale outputs_ on reload
a9ef11a2b3