* test(skills): skip the skill-export capture suite where fd-based walking is unavailable
export._capture intentionally rejects every export with 422
skill_export_unsupported on platforms without os.O_NOFOLLOW and dir_fd
directory walking (Windows), so the 40 capture-dependent tests in
test_skill_export.py and test_gateway_skill_export.py fail there. Add a
requires_safe_capture mark mirroring the production feature guard and
apply it to those tests; the 21 tests that only exercise the zip
installer, export lock, or router plumbing keep running.
* test(skills): share requires_safe_capture and cover the blocking-io export suite
Move the mirror of export._capture's platform guard into
tests/support/skill_export_platform.py so the per-file copies cannot
drift, and apply it to blocking_io/test_skill_export.py::test_export_worker_and_response_are_off_loop,
which drives the real exporter and hits the same 422
skill_export_unsupported guard on Windows (the blocking-io suite is
excluded from the default make test run).
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>