Add Windows smoke test for winget install

[ChrisonSimtian]

Parent: #121

End-to-end smoke test in CI on windows-latest exercising the install path operators will actually use.

Definition of done

GH Actions job that, on a manual dispatch and on release-candidate tags:

1. Validates the local winget manifest (W1) against the candidate installer (W2).
2. Installs from the local manifest via winget install --manifest.
3. Asserts the FalloutAgent service exists and starts (W3).
4. Runs a mocked coordinator handshake — agent reaches a local stub, returns "enrolled".
5. Uninstalls via winget uninstall Fallout.Agent; asserts the service is gone and %ProgramData%\Fallout\Agent\ is cleaned per spec.
6. Job exits 0 only if all six steps succeed.