add pir: fuzzy-find and resume pi sessions for the current dir

`pi -c` blindly grabs the newest session, and the alternative is digging
through ~/.pi/agent/sessions/--home-user-dev-foo--/ for a UUID by hand.
This lists every session for the cwd in an fzf picker with a live transcript
preview and execs `pi --session <file>` on the pick.

  pir              pick a session for this dir
  pir -a           pick across every project dir
  pir <query...>   start fzf with an initial query
  pir -g TEXT      only sessions whose full transcript contains TEXT

The -g pass exists because the fzf query matches the list line -- title and
id -- not deep history, so "the session where I fixed the mouse bug" is
unfindable without it. It shells out to rg when available and falls back to
grep.

In the picker: enter resumes, ctrl-f forks instead (execs --fork, leaving the
original untouched), ctrl-o prints the path and exits without launching,
ctrl-a toggles current-dir vs all-dirs, ctrl-s toggles recent vs longest.
The toggles are fzf --bind=reload of this same script, which is what --list
and --preview are for -- they are internal modes invoked by fzf, not user
entry points.

Session directory resolution mirrors pi's own getDefaultSessionDirPath()
encoding, and honours PI_APP_NAME / <APP>_CODING_AGENT_DIR, so a renamed or
relocated agent dir still resolves. Forked sessions are detected from the
header's parentSession and marked in the list.

Requires fzf; checked up front with a clear error rather than failing inside
a pipeline.

0 files changed, 0 insertions, 0 deletions