Update application with new icon

[Gabriel Dufresne (GabrielDuf)]

Replaces the UniGetUI icon (blue layered-stack glyph) with the new Devolutions UniGetUI icon everywhere it appears, across both the WinUI and Avalonia front-ends, and reworks the system-tray icon to a single legacy style.

App icon (all sizes/formats, regenerated from the new master SVG)

• WinUI app/window/taskbar icon: icon.ico (root + Assets/Images), plus icon.png, icon.bmp, icon_unsquare.png
• Windows Store tiles: Square150x150Logo, Square44x44Logo, StoreLogo, Wide310x150Logo
• Splash screens (light + dark, .svg + .png): new icon tile swapped in, the "Devolutions UniGetUI" wordmark kept
• Repo media assets: media/icon.png, store.png, socialicon.png, every media/Icon sizes/*, and the canonical media/assets brand SVG

System tray: legacy-only + setting removed

• The tray now always uses the legacy status icons on every platform (WinUI + Avalonia). The status-dot color system is unchanged (up-to-date / updates / in-progress / attention / restart).
• Removed the user-selectable Tray icon style setting and its selector UI on both front-ends, dropped the Settings.K.TrayIconStyle key, and deleted the now-unused colored/monochrome tray .ico assets along with their Avalonia <AvaloniaResource> entries.