The `i-` prefix install option was a holdover from the multi-skill era.
With a single `impeccable` skill it only ever renamed that one skill to
`i-impeccable`, while the install message wrongly advertised `/i-audit`
style commands that never existed, and the unscoped rename could clobber
unrelated third-party skills in the same harness folder.
- Drop `--prefix=`, the interactive prompt, and all prefix machinery
(renameSkillsWithPrefix, prefixSkillContent, detectPrefix, undoPrefix,
prefixedCommandHint, isImpeccableSkillName).
- Add migrateUnprefixImpeccable: install --force and update rename any old
`<prefix>impeccable` back to canonical `impeccable` before the fresh copy
lands, scoped by name so foreign `i-*` skills are left untouched.
- Fix FAQ + editorial that wrongly described pinned commands as `i-`
prefixed (pins are bare `skills/<command>/` dirs).
- Tests now exercise the real exported migration, not a reimplementation.
- CLI 2.3.1 -> 2.3.2 with a changelog entry.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>