Plan B Phase 3 sub-step 1. The new helpers collapse the
Option<T>::map(Ok).unwrap_or_else(|| prompt(...))? chain that
the seven build_*_item builders repeat. Reader is injectable
via the *_with_reader variants so the unit tests can drive
both the flag-value and prompt paths from a Cursor without
needing a TTY. prompt and prompt_optional are refactored to
delegate to two private read_*_line helpers; semantics are
unchanged. dead_code is allowed on the four new helpers
until sub-step 2 wires them into commands/add.rs.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
