Enable Windows targeting for Linux builds

[Vaso73]

Summary

• Add EnableWindowsTargeting=true to the main QuickSSH project.
• Add EnableWindowsTargeting=true to the QuickSSH test project.
• This allows Windows-targeted QuickSSH projects to restore/build from a Linux LXC development environment.

User-facing impact

• This PR changes user-facing behavior
• This PR adds or changes commands
• This PR changes installation, shell, config parsing, import/export, or profile behavior
• README.md was updated if required

No user-facing behavior change. This is a development/build configuration change only.

Release intent

• release:patch
• release:minor
• release:major
• skip-release

Validation

• CI passes
• Tests were added or updated when needed
• Workflow files remain aligned with current main

Manual validation from Debian LXC:

dotnet build Flow.Launcher.Plugin.QuickSSH.csproj --configuration Release