fix(installer): set EnableWindowsTargeting so Linux Gitea runners can publish

The release workflow runs on a Linux container; building net8.0-windows +
UseWPF=true requires this opt-in property since .NET 8. No-op on Windows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ClaudeDo.Installer.Tests/ClaudeDo.Installer.Tests.csproj

@@ -7,6 +7,8 @@
 
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
+    <!-- Allow Linux Gitea runners to build this Windows-targeted project; no-op on Windows. -->
+    <EnableWindowsTargeting>true</EnableWindowsTargeting>
   </PropertyGroup>
 
   <ItemGroup>