Nested PTY processes shut down gracefully; TUI force shutdown restored

<!-- Release notes generated using configuration in .github/release.yml at v2.9.19-canary.8 -->

What's Changed

Changelog

• fix: Remove accidental shell commands example changes by @anthonyshew in https://github.com/vercel/turborepo/pull/13094
• release(turborepo): 2.9.19-canary.7 by @github-actions[bot] in https://github.com/vercel/turborepo/pull/13095
• fix: Refine graceful shutdown messaging by @anthonyshew in https://github.com/vercel/turborepo/pull/13098
• fix: Gracefully stop nested PTY processes by @anthonyshew in https://github.com/vercel/turborepo/pull/13100
• fix: Restore TUI force shutdown by @anthonyshew in https://github.com/vercel/turborepo/pull/13102

Full Changelog: https://github.com/vercel/turborepo/compare/v2.9.19-canary.7...v2.9.19-canary.8