docs: polish pass for permissionless-architecture update

[grimnote]

Summary

• Polish relayer/operator terminology across the permissionless settlement docs
• Remove stale relay-fee spec framing and deleted CCTPHandler references
• Smooth prose seams left by the operator-stack deletion and drop the hand-off note

Checks

• npx prettier --check .
• npm run lint
• npm run build
• npm run test
• grep stale-term self-check: only remaining "exclusive window" hits are negations