Fix devolutions icon not showing

[Gabriel Dufresne (GabrielDuf)]

Summary

• Replaced 8 SVG icon URLs for Devolutions products inscreenshot-database-v2.json with PNGs hosted in this repo,
  since the package-icon renderer (new Bitmap(...) on Avalonia and BitmapImage on WinUI) only supports raster formats — SVGs were downloaded into the cache but failed silently when bound to the Image controls, so RDM, Workspace, Agent, Gateway, Jetsocat, Launcher, ServerConsole, and RDM Agent showed no icon.
• Added an icon for Devolutions.MsRdpEx (rasterized from msrdcex.ico in the Devolutions/MsRdpEx repo), which previously had an empty icon field.
• Brought Avalonia package-list icon sizes in line with WinUI — every layout was ~33% smaller. Compact list 16→24, card 36→44, grid/icons 48→64 (with the same -8,0,0,4 margin trick WinUI uses to fit a 64px icon in a 60px row), and the column metadata icons in the compact view (Id, Version, NewVersion download/warning, Source) 16→24.