Clean up UI for WinUI and Avalonia

[Gabriel Dufresne (GabrielDuf)]

This pull request makes several UI improvements to the application, focusing on the layout and controls of the packages page, sidebar, and main window.

Packages Page Layout and Controls:

• Moved the "Order by" and "View mode" controls from the header to a new footer status bar, improving clarity and freeing up header space.
• The "Reload" button is now added programmatically to the toolbar, with its tooltip text bound to a translatable resource.

Sidebar Improvements:

• The user avatar has been moved from the main window's title bar to the sidebar's footer for a more standard navigation experience.
• All sidebar menu items now feature clear, consistent SVG icons, improving visual navigation and accessibility.

Main Window and Avatar Handling:

• The avatar display control has been updated to use a circular border for a modern look.

Other UI Tweaks:

• Minor toolbar adjustments on the Discover Software page, such as removing a duplicate help button.