docs: clarify demo interpretation framing

[rlippmann]

What changed

• Simplified interpretation wording in README.md, demos/README.md, and docs/demos-results.md.
• Clarified that demos 01–05 and 07 focus on persistence/policy-following behavior.
• Clarified that demos 08/09 focus on host-side transition checks and architectural capability boundaries.
• Clarified that baseline/reinjected-state can produce plausible responses and still fail transition checks.

Why

• Reduce benchmark/leaderboard-style interpretation of demos 08/09.
• Keep documentation behavior-first and aligned with repo docs-style guidance.

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)