refactor(artifacts): harmonize Windows to Linux raw-file collection

Windows produced an intermediate C:\CI\output\artifacts.zip that
upload-artifact then re-zipped (zip-in-zip), while Linux deposited raw
files. Make both paths consistent: the build stages raw outputs into a
collect dir; collect zips it only as a transport archive, fetches, and
extracts into the host artifact dir; actions/upload-artifact produces
the single final archive.

- _windows_build: param artifact_zip -> output_dir; stage raw files
  (in-place when source IS the collect dir, else wipe+copy), no
  Compress-Archive; absolute artifact-source resolved.
- _windows_collect: zip guest dir as transport, fetch, extract (mirror
  _linux_collect); guest_path is now the collect directory.
- job.py / build_run CLI: pass output_dir; rename --guest-artifact-zip
  -> --guest-output-dir.
- Tests updated for the raw-file contract.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/python/test_commands_job.py

@@ -322,8 +322,8 @@ def test_job_windows_branch_with_overrides(
     # CPU/RAM override patched the clone VMX.
     clone_vmx = next((tmp_path / "vms").rglob("*.vmx"), None)
     # After successful job the clone dir is deleted, so the file is gone.
-    # Check that the Windows collect helper got the correct artifact path instead.
-    assert calls["windows_collect"][0]["guest_path"].endswith("artifacts.zip")
+    # Check that the Windows collect helper got the collect dir instead.
+    assert calls["windows_collect"][0]["guest_path"] == "C:\\CI\\output"
     assert clone_vmx is None  # cleaned up
     assert backend.calls[-1] == "delete"