Fix package workflow publishing inputs

[Copilot]

The package GitHub Actions job failed while building the WiX installer because HaActiveUser.SessionAgent.exe was not published before MSI creation.

• Publish inputs

  • Replace the single-project dotnet publish step with the existing packaging script:

    - name: Publish agents
      run: pwsh ./build/publish-agent.ps1 -SkipInstaller

  • This produces both installer inputs: the service agent and session tray agent.

• Signing

  • Add a signing step for HaActiveUser.SessionAgent.exe so both packaged executables follow the same pre-MSI signing flow.