Add automatic updates for portable releases

[Wraiith32]

Summary

• Replace the notification-only update check with an Onova-based update service.
• Download and install the existing TarkovMonitor.zip release asset automatically after user confirmation.
• Restart TarkovMonitor after applying an update.
• Ensure release tags set the correct executable version.
• Add a PowerShell script and documentation for end-to-end local update testing.

Existing users must manually install the first release containing this change. Future releases can then update automatically.

Screenshot of the update prompt:

[Wraiith32]

It appears two of us had the same idea. There are two auto-update options now. See #222