feat: add versioned reduction specifications

[fly1d]

Summary

• add a strict schema_version: 1 JSON reduction specification shared by Reduce and Doctor
• expose the same configuration contract through the GitHub Action with workspace-confined portable paths and fail-closed input ownership
• align Doctor baseline sampling and Docker resource validation with reduction behavior
• document schema fields, defaults, migration, security boundaries, and Action usage

Validation

• PYTHONPATH=src python3 -m unittest discover -s tests -q (699 passed, 2 skipped)
• installed wheel suite (699 passed, 2 skipped)
• installed sdist suite (699 passed, 2 skipped)
• 16 offline benchmarks (16 passed, 0 skipped, 0 failed)
• ruff check src tests scripts benchmarks
• python scripts/check_contribution.py --skip-tests
• python scripts/check_docs.py
• isolated PyYAML parsing for action.yml and .github/workflows/ci.yml
• bash -n for both composite Action Bash blocks
• python -m twine check plus release-artifact and archive-content validation
• git diff --check

Release scope

This PR does not create a tag, GitHub Release, or PyPI publication. PYPI_PUBLISH_ENABLED remains disabled.