[cestercian]

Summary

Adds -print, which writes just the suggested command to stdout and exits. No menu, nothing runs, and stdin is never read. The cases that would normally prompt (missing key, rejected key, a reply that is not a command, a reply with hidden characters) return an error instead, so they exit 1 with the message on stderr.

Docs are updated in -h, the README (with a note that piping into a shell skips confirmation), the man page and the bash/zsh/fish completions.

Related issue

Closes #14

Type of change

• Bug fix (fixes a problem without changing intended behavior)
• New feature (adds functionality without breaking existing usage)
• Breaking change (changes existing flags, environment variables, output or exit codes)
• Documentation only
• Tests, CI, build or refactoring (no user facing change)

Checklist

• I added or updated tests for this change.
• make test and make lint pass locally.
• I added an entry under ## [Unreleased] in CHANGELOG.md for user facing changes.
• I updated the docs (README.md, aiterm -h help text) where needed.
• My commits and the pull request title follow Conventional Commits.

Tests use chatServer with a stdin reader that fails the test if it gets read, plus two new -print cases in TestMainExitCodes.