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_build.py

@@ -360,5 +360,6 @@ def test_build_run_windows_host_source_dir(
     assert instance.copies[0][1] == "C:\\CI\\src-transfer.zip"
     cmds = [c[0] for c in instance.runs]
     assert any("Expand-Archive" in c for c in cmds)
-    # Packaging step references the configured artifact source dir.
-    assert any("Compress-Archive" in c and "'dist'" in c for c in cmds)
+    # Staging copies the raw source into the collect dir (no zip-in-zip).
+    assert any("Copy-Item" in c and "'dist'" in c for c in cmds)
+    assert not any("Compress-Archive" in c and "'dist'" in c for c in cmds)