feat(hooks): surface leftover post-commit hooks (#167 follow-up) (#172)

A post-commit hook installed by codeindex < 0.37 survives the upgrade
silently: the dead wrapper errors into ~/.codeindex/hooks/post-commit.log
(|| true swallows the exit code) while every commit still pays one
Python startup. Nothing showed it — status only iterated
SUPPORTED_HOOKS, and uninstall --all likewise skipped it.

- hooks status: flags a codeindex-managed post-commit with the exact
  cleanup command (RETIRED_HOOKS seam for future retirements)
- hooks uninstall --all: removes the leftover along with supported hooks