Make Windows qualification cleanup deterministic

[dovvnloading]

Summary

• capture cleanup exceptions inside the bounded qualification thread instead of emitting an orphaned traceback
• retry temporary workspace deletion while native Windows process handles settle
• add regression tests for cleanup exception capture and transient deletion failures

Validation

• python -m pytest -q (368 passed, 1 skipped)
• python -m ruff check tools/execution_spikes/recipe_worker_e2e_qualification.py tools/execution_spikes/recipe_coordinator_e2e_qualification.py tests/test_phase2_recipe_coordinator_qualification.py