Render SVG instead of PNG in the About window

Currently, because of the SVG story around Avalonia being a bit too confusing (different versions of SkiaSharp being refrenced by Avalonia itself and Svg.Controls.Skia.Avalonia), I've decided to rely on the 256 px `.png` icon in the **About** window for now.

We'll need to investigate the full compatibility story here and migrate to using of the SVG icon.

See `TODO[#80]` in the code to find the relevant places.

Locate the TODO[#80] markers to find the relevant About-window code and inspect how Avalonia, SkiaSharp, and Svg.Controls.Skia.Avalonia versions interact. Confirm the compatibility constraints, then verify that the About window renders the SVG icon instead of the 256 px PNG and that the result displays correctly.

Written by the indexing model from the issue text.