Polish README and landing page copy

[ictechgy]

Summary

• polish root/plugin/kit README wording for setup, savings-claim boundaries, and agent surfaces
• tighten brief-mode and mac prototype README phrasing
• refine Korean landing page copy without changing feature claims or runtime behavior

Validation

• python3 - <<'PY' ... HTMLParser().feed(docs/index.html) ... PY
• python3 scripts/prepublish_check.py --skip-tests
• python3 scripts/release_smoke.py --timeout 20
• git diff --check

[ictechgy]

Claude follow-up editorial pass completed.

Artifact:

• .omx/artifacts/claude-you-are-reviewing-pr-208-for-contextguard-the-user-asked-for-2026-06-15T21-51-29-472Z.md

Result:

• Applied Claude's one must-fix suggestion: README.ko.md now uses 간결한 요약 기록 instead of 작은 요약 기록.
• Claude found the claim-boundary language preserved and recommended keeping the conservative no-guaranteed-savings / no-external-offload wording unchanged.

Revalidated:

• HTMLParser parse of docs/index.html
• python3 scripts/prepublish_check.py --skip-tests
• python3 scripts/release_smoke.py --timeout 20
• git diff --check