v0.1.22

Prune worktree disk: hooks/prune, dangle prune, and sizes in list

Every worktree keeps its own build output and nothing ever collects it; a merge-queue
worktree in one project reached 238 GB. dangle now owns the policy:

- hooks/prune <worktree> <days>: the project says what is disposable.
- dangle prune [-n] [--days N] [--max-gb N] [--all] [--rm]: run it now; --rm also drops
  plan worktrees with no commits of their own and no untracked files.
- Automatically at the start and end of a run, for worktrees idle PRUNE_DAYS days or over
  PRUNE_MAX_GB, never one in use, with changes, or the one you stand in.
- dangle list shows each worktree's size.

DANGLE_PRUNE_DAYS and DANGLE_PRUNE_REASON tell the hook why it runs.
dangle 0.1.22