chore(release): prepare v0.1.2

[muxx]

Summary

• bump all SDK and CLI packages to 0.1.2
• refresh Python lock files and generated reference manifest
• update the Go runtime smoke test for the current Sandbox.Kill contract

Verification

• frozen pnpm/uv installs
• format, lint, typecheck, and JavaScript/Python tests
• Go build, test, race, coverage, and external-consumer checks
• deterministic generation
• release artifact build and clean-install smoke tests
• full KVM release-runtime suite for JS, Python sync/async, CLI, Go, and Code Interpreter