Add hotspot settings window and tray integration

[AghastyGD]

Summary

This PR introduces the first settings interface for wiretray.

Users can now open a dedicated settings window from the tray menu, configure hotspot settings, and manage hotspot state without relying on hardcoded values.

What's included

• Add a GTK4-based settings window.
• Add a Settings action to the tray menu.
• Allow editing and saving hotspot SSID and passphrase.
• Validate hotspot passphrases before saving.
• Display the current hotspot status in the settings window.
• Add start and stop hotspot actions directly from the settings window.
• Keep the UI synchronized with NetworkManager state changes.
• Introduce a dedicated wiretray-settings binary.

Notes

This is the first step toward a complete desktop configuration experience.

The current interface focuses on basic hotspot configuration, while providing a foundation for future features.