fix(studio): normalize Codex sandbox tool names

[evanlowe]

Summary

• use codex as the purpose segment for newly provisioned Codex sandbox Tools
• reuse existing chat-named CodeEnv Tools as a compatibility fallback
• apply the same behavior to regular deploys, snapshots, self-update, and BytePlus repair flows

Testing

• pre-commit run --show-diff-on-failure --color=never --all-files
• pytest targeted Studio provisioning and update suites: 103 passed
• full pytest suite: 1566 passed, 5 skipped; two stdio MCP tests affected by parallel process startup passed on serial rerun