refactor(cockpit): clarify runtime customization boundaries

[x-lixu]

Summary

• preserve previously completed realtime recovery and cockpit custom-skill work
• promote runtime voice switching to the Gateway Client Protocol and SDK
• reorganize the smart-cockpit example around clear client, gateway, agent, service, and bootstrap ownership
• separate client-facing persona/voice choices from trusted Gateway prompts and colocate module tests
• update bilingual contracts, protocol docs, scenario guides, and test matrices

Verification

• npm run test:smart-cockpit
• npm run example:smart-cockpit:lint
• npm run example:smart-cockpit:build
• npm run lint -- --quiet
• git diff --check