✨ Complete: always_on_top configuration and controls

[mx57]

This change completes the missing/half-baked always_on_top configuration feature in Desktop Pet Cat.
By integrating always_on_top fully into ConfigManager, PetWindow, SettingsDialog, and TrayMenu, we have provided a seamless and highly interactive user experience.

🎯 What was added:

• In PetWindow's initialization, respect the config's always_on_top setting (default: True).
• Implement dynamic set_always_on_top toggling that handles PySide6's window flags and re-shows the window.
• Add "Поверх всех окон" QCheckBox in SettingsDialog to view/edit settings.
• Add "Поверх всех окон" checkable QAction in TrayMenu for quick toggle with synchronization across the system.
• Add thorough unit testing for the new functionality.

📋 Checklist:

• Initial window flag initialization based on configuration
• PetWindow.set_always_on_top(enabled) implementation
• SettingsDialog QCheckBox integration and saving
• TrayMenu checkable QAction integration and sync
• Unit tests added and verified

🧪 Testing:
Run all tests using: PYTHONPATH=. python3 -m unittest discover tests

---

PR created automatically by Jules for task 14400016884025613417 started by @mx57

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.