fix(packaging): add PackageReadmeFile to RuntimeOverride for snupkg

NU5017 'Cannot create a package that has no dependencies nor content'
fired during dotnet pack because the snupkg has only loose .pdb files
under runtimes/ — the symbol packager doesn't count those as content.

The .nupkg packs fine (it has the runtime DLLs). To make snupkg succeed,
add a PackageReadmeFile pointing at the existing README.md and Pack the
file. This also resolves the secondary 'package is missing a readme'
NuGet best-practice warning.

InitialForce.WPF.csproj already does this; alignment now matches.

Author: Claude (Initial Force WPF Bot)

packaging/InitialForce.WPF.RuntimeOverride/InitialForce.WPF.RuntimeOverride.csproj

@@ -31,8 +31,17 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <!-- Suppress warnings for NoBuild SDK-style packaging. -->
     <NoWarn>NU5128</NoWarn>
+    <!-- Required so dotnet pack does not emit NU5017 for the snupkg
+         (a symbol package needs at least one piece of content; loose
+         PDBs alone in runtimes/ are not counted). -->
+    <PackageReadmeFile>README.md</PackageReadmeFile>
   </PropertyGroup>
 
+  <!-- Pack the README. -->
+  <ItemGroup>
+    <None Include="README.md" Pack="true" PackagePath="README.md" />
+  </ItemGroup>
+
   <!-- Empty placeholder assembly: makes the package referenceable in projects
        that check for compile-time assets. The real DLLs are under runtimes/. -->
   <ItemGroup>