Show the recorded two-chat demo in the README

[momonpya]

Summary

Embed the approved 29-second Codex CLI demo near the top of the README, so visitors can see findings carried into an independent chat. Add the matching demo guide and sanitized measurement record: 81.8% fewer input-plus-output tokens in the second chat in this recorded pair, with the static source review and comparison limits stated alongside the result.

Why

The README previously linked to an edited walkthrough. The recorded CLI demo shows the actual handoff and token comparison directly, with supporting counts and evidence hashes. This changes three documentation files only.

Verification

• GitHub's native README video player loaded and reported a 29-second duration.
• Checked the measurement JSON totals and second-chat reduction arithmetic.
• git diff --check origin/main...HEAD passed.
• Documentation and measurement limits are included.
• Performance claims report input plus output tokens and answer-review limits.
• Linux and macOS CI passed: Lean build, core tests, lifecycle regressions, package checks, installer syntax, and the two-chat sample.
• Linux and macOS adapter contract CI passed, including native adapter and OpenCode checks.