Replace the package logo for both packages

[Smaug123]

Vectorises the new reference raster in logos/ with potrace 1.16 (the route the other WoofWare packages took) into a light/dark pair whose only difference is the fill attribute, displays them in the README via <picture>, and packs a 1024x1024 PNG rendering as the PackageIcon of both WoofWare.Myriad.Plugins and WoofWare.Myriad.Plugins.Attributes, which shared the old one.

The readme

The logo was previously a plain Markdown image with a relative path. nuget.org does not resolve relative image paths, so it rendered there as a broken image. It cannot show a <picture> element either: it renders the packed readme through Markdig configured with DisableHtml(), which removes the HTML block parser rather than sanitising, so raw HTML falls through to a paragraph and is escaped — the element would appear as literal tags. So each project's pack writes a copy of the readme with that element removed into its intermediate output directory and packs that, leaving PackageIcon to carry the logo on nuget.org. This is the same mechanism as the other WoofWare packages.

The strip runs as a RoslynCodeTaskFactory inline task rather than through WriteLinesToFile, because that task takes items and MSBuild normalises directory separators in an item spec — which silently rewrote a backslash in a sibling repo's readme. It checks its own postcondition (that no <picture> survived) and fails the pack if the strip did not take, which also makes it safe for the element to grow attributes.

version.json

The logo moves out of the WoofWare.Myriad.Plugins directory, so both version.json path filters have to follow it — the Attributes one named :/WoofWare.Myriad.Plugins/logo.png explicitly, and the Plugins one covered it implicitly through ./. Without the new :/logos/light.png entries, a future logo change would no longer bump either version height.

Verification

• Both nupkgs differ from the ones main produces only in logo.png becoming light.png; both declare <icon>light.png</icon>.
• Each packed readme is exactly the readme minus its <picture> element, and rendering it through the same Markdig pipeline nuget.org uses leaves no escaped tags outside code blocks.
• The destination path resolves correctly both by default (obj/) and under UseArtifactsOutput (artifacts/obj/).
• The postcondition check was mutation-tested against real packs, per project: breaking one project's strip pattern fails that project's pack while the other still packs, an unclosed element fails both, and both strip <picture class="logo"> correctly.
• Full suite passes: 1272 tests.

Unrelated observation, not addressed here

<None Include="$(OutputPath)\*.dll" ... /> in WoofWare.Myriad.Plugins.fsproj is a wildcard evaluated at project-evaluation time, before the build populates bin/. Packing a clean checkout therefore produces a package with only WoofWare.Myriad.Plugins.dll under lib/net6.0/, while packing a warm tree produces all ten DLLs. I measured this on main as well as on this branch, so it is pre-existing and unchanged by this PR — but it does mean the package contents depend on the state of the build directory. Happy to fix separately if you want.