The README one-liner piped the downloaded installer into `bash -s`, so the
script's stdin was the script itself. `confirm_setup` requires a terminal
stdin, which meant a user running the documented command from a real
terminal was never offered the private CLI or a Plasma restart. Run the
installer with `bash -c` instead: stdin stays the terminal, and nothing can
consume the rest of the script from the pipe. Non-terminal runs remain
non-interactive.

A setup test now runs the README command verbatim under a pseudo-terminal
and without one; it fails with the previous command.

Documentation: README command, development setup notes, CHANGELOG.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>