fix: harden setup tui rendering

[anand-testcompare]

Summary

• remove the OpenTUI conditional render shape that produced orphan text nodes in setup
• keep mouse capture disabled and add explicit Esc/Ctrl+C exit guidance in the setup wizard
• add a packaged TUI smoke check to CI so installed setup rendering is exercised before publish
• document the setup exit controls in the README

Testing

• bun run check
• bun run typecheck
• bun test
• bun run build
• npm pack --pack-destination .memory/release-check
• local installed tarball help + TUI smoke in sandcode-testing