Fixes: ResolvePackageAssets fails with "Unable to find fallback package
folder 'D:\Microsoft Visual Studio\Shared\NuGetPackages'".
That folder comes from a machine-wide Visual Studio installer config
(C:\Program Files (x86)\NuGet\Config\Microsoft.VisualStudio.FallbackLocation.config),
not from anything in this repo — it points at a fallback package cache on
whatever drive VS was originally installed on, and NuGet fails outright if
that path doesn't exist on the current machine. nuget.config already had
<clear/> under packageSources for the same reason (pin restore to nuget.org
only); it just didn't do the equivalent for fallbackPackageFolders. Restore
and build now depend only on this file, not on machine-specific VS install
history.
- Move all .NET (6 projects, solution, Directory.*.props, nuget.config)
into backend/ so the monorepo root can host non-.NET projects later
- Remove throwaway test artifacts: player.html, pl.json
- Trim dead Flutter rules from .gitignore
Build from backend/Musify.slnx: 0 warnings, 0 errors.