chore: drop branch-local design docs and revert githook worktree fix

- Remove docs/superpowers/{plans,specs} — these were branch-local design
  artifacts that don't belong in the upstream PR.
- Revert githook.cjs to its pre-branch state. The worktree-aware
  resolver was only needed to make `npm install` succeed in this
  development worktree; it is not core to the CMCD upgrade.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: littlespex