Choose sample trajectory and verify license

[kkkniengLiu]

Seed issue from OpenSciFlow Day-1 plan. See repository ISSUES.md and MILESTONES.md for context.

[kkkniengLiu]

Added the first MVP sample-data guardrails in main:

• docs/sample-data-policy.md
• docs/demo-runbook.md
• examples/protein-md-stability/sample-data-checklist.md
• examples/protein-md-stability/sample-run-manifest.json now records sample_data provenance fields.

Current preferred candidate is MDAnalysisData adk_equilibrium, but it remains a candidate until the exact dataset license, citation, file sizes, and SHA256 hashes are recorded from the dataset metadata.