Fix Windows installer fixture

[calvin-archastro]

Review on ArchCode

Problem and author intent

The initial public-repository installer workflow generated Windows fixtures with PowerShell 7 Add-Type -OutputType ConsoleApplication. PowerShell 7 rejects that output type, so the fixture build stopped before the installer boundary ran. The repository needs a runnable Windows fixture so its installer gate proves both packaged executables survive download, checksum verification, extraction, and installation.

What changed

• Compile the fixture with Windows' framework C# compiler, which emits a runnable console executable on the hosted Windows runner.
• Keep the CLI and dashboard fixture behavior identical: both print the requested version.
• Move checkout to the pinned Node 24-based v7 action.

Scope

CI and test-fixture only.

Risk assessment

Low. The change affects only generated test fixtures and CI checkout. Release binaries and installers are unchanged.

User impact

No direct user-facing change. The public installer gate now catches non-runnable Windows packages.

Testing

• Canonical end-to-end proof: .github/workflows/installer-smoke-test.yml, job Windows Installer. It builds the fixture, crosses a real localhost HTTP download boundary through install.ps1, verifies the checksum, installs both executables, runs both installed processes, and asserts version 0.31.0.
• YAML parsing and diff checks pass locally.
• The GitHub-hosted Windows result is the required merge gate.

Follow-ups and known issues

None.