Record node status snapshots before runs

[yoshifuminakamura]

Summary:

• record a scheduler-neutral node status snapshot before benchmark runs
• store the full snapshot as a measurement artifact while keeping Result JSON to summary, hash, and artifact reference
• show the snapshot only on the console detail surface; keep it hidden from the public surface

Validation:

• .venv/bin/python -m pytest result_server/tests/test_result_detail_template.py result_server/tests/test_measurement_artifacts.py result_server/tests/test_result_padata_route.py result_server/tests/test_public_result_routes.py result_server/tests/test_api_routes.py
• bash scripts/tests/test_node_status_snapshot.sh
• bash scripts/tests/test_process_and_send_results.sh
• bash scripts/tests/test_result_common_json_contract.sh
• bash scripts/tests/run_profile_data_shell_tests.sh common
• bash -n for touched shell scripts
• shellcheck -S error for touched shell scripts
• git diff --check

Review note:

• checked the PR diff for sensitive or environment-specific values; the public surface does not expose this artifact.