fix: prevent duplicate layer surfaces on monitor hotplug

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

include/client.hpp

@@ -56,6 +56,8 @@ class Client {
   std::list<struct waybar_output> outputs_;
   std::unique_ptr<CssReloadHelper> m_cssReloadHelper;
   std::string m_cssFile;
+  sigc::connection monitor_added_connection_;
+  sigc::connection monitor_removed_connection_;
 };
 
 }  // namespace waybar