This PR implements complete Linux support for the TrayManager class, providing system tray functionality on Linux platforms using GTK3.

What's implemented

TrayManager (src/platform/linux/tray_manager_linux.cpp)

• Creates and manages system tray icons using GTK StatusIcon
• Provides thread-safe unique ID generation for tray instances
• Implements Create(), Get(TrayID), and GetAll() methods matching the existing interface

Tray (src/platform/linux/tray_linux.cpp)

• Full system tray icon functionality using GTK StatusIcon APIs
• Icon support for base64 encoded images, file paths, and stock GTK icons
• Title and tooltip functionality with proper GTK widget integration
• Context menu support with Menu object lifecycle management
• Bounds detection using GTK geometry APIs
• Proper resource cleanup using the pimpl pattern

Menu (src/platform/linux/menu_linux.cpp)

• GTK menu and menu item implementations
• Support for adding/removing items and separators
• MenuItem creation with title, icon, and tooltip support
• Native GTK menu widget access for integration

Example usage

#include "tray_manager.h"

// Create tray manager
nativeapi::TrayManager trayManager;

// Create a new tray
auto tray = trayManager.Create();
tray->SetTitle("My App");
tray->SetTooltip("Application running in background");
tray->SetIcon("gtk-info");  // Stock icon or file path

// Create context menu
nativeapi::Menu menu;
auto menuItem = menu.CreateItem("Exit");
menu.AddItem(menuItem);
tray->SetContextMenu(menu);

Technical details

• Uses GTK3 StatusIcon (though deprecated, still widely supported across Linux desktop environments)
• Implements proper base64 image decoding with automatic scaling to 24x24 pixels
• Maintains API compatibility with existing macOS implementation
• Follows the established pimpl pattern for clean platform abstraction
• All implementations compile successfully and pass basic functionality tests

The implementation provides feature parity with the macOS TrayManager while leveraging native Linux desktop integration through GTK3.

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