Add Restart and Exit actions to tray icon menu

[Yanitwei]

Summary

Adds a native context menu to the system tray icon with:

• Restart
• Exit

Details

• Preserves existing left-click behavior for showing and hiding the tray window.
• Reuses the application's existing graceful shutdown path for Exit.
• Implements Restart by relaunching the current executable after shutdown.
• Keeps updater-driven restart behavior separate to avoid duplicate launches.

Testing

Tested on Windows:

• Application builds successfully.
• Tray icon appears normally.
• Left-click continues to toggle the window.
• Right-click displays the context menu.
• Exit closes the application cleanly.
• Restart closes and relaunches the application successfully.

[snekxs]

Superseded by #14 (same change, rebased onto current main plus a clippy fixup for the 8-arg constructor — your fork was behind main and I can't push to it). #14 is merged. Closing this one.