Migrate from C++ Qt to Rust and COSMIC

[azdanov]

Migrate the Package Installer from C++ Qt to Rust using the COSMIC toolkit to align with modern Linux desktop standards and improve maintainability.

Useful Links

• libcosmic – UI toolkit
• cosmic-app-template – Reference implementation

To do

• Set up Rust project structure using libcosmic
• Port core package management logic
• Implement COSMIC-native UI (responsive, dark/light theme support)
• Testing and release packaging