[WIP] [Linux] Implement Tray class

[Copilot]

Implementation plan for Linux Tray class:

Task: Implement Linux Tray class

• Analyze repository structure and existing implementations
• Understand macOS implementation pattern (pimpl with Impl class)
• Identify required GTK dependencies (already installed)
• Plan implementation approach using GTK3 system tray

Implementation Plan:

• Create src/platform/linux/tray_linux.cpp - Tray class implementation
• Create src/platform/linux/tray_manager_linux.cpp - TrayManager class implementation
• Implement all required methods:
  • Constructor/destructor with GTK StatusIcon
  • SetIcon/GetIcon (including base64 support)
  • SetTitle/GetTitle
  • SetTooltip/GetTooltip
  • SetContextMenu/GetContextMenu
  • GetBounds
• Build and test implementation
• Create simple test to verify functionality

Technical Approach:

• Use GTK3's GtkStatusIcon for system tray implementation
• Follow the same pimpl pattern as macOS implementation
• Handle base64 image data similar to macOS version
• Ensure thread safety and proper GTK integration

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