Add event listening stubs to TrayIcon for Linux

Introduces StartEventListening and StopEventListening methods to TrayIcon on Linux. These methods are placeholders, as AppIndicator manages events automatically and no additional setup or cleanup is required.

Author: lijy91

src/platform/linux/tray_icon_linux.cpp

@@ -252,4 +252,14 @@ void* TrayIcon::GetNativeObjectInternal() const {
   return static_cast<void*>(pimpl_->app_indicator_);
 }
 
+void TrayIcon::StartEventListening() {
+  // Called automatically when first listener is added
+  // AppIndicator handles events automatically, no platform-specific setup needed
+}
+
+void TrayIcon::StopEventListening() {
+  // Called automatically when last listener is removed
+  // AppIndicator handles events automatically, no platform-specific cleanup needed
+}
+
 }  // namespace nativeapi