stop tracking .pql/hooks — finish T-28 decommission

pql 1.4.x bakes the absolute path to the pql binary into each hook
when init plants them. Tracking the hooks made every developer's
init produce a permanent dirty diff against the committed paths.
The right fix per T-28 is to never track them: each clone's
'pql init' plants its own hooks locally, nothing tracked, no drift.

Drops:
- !.pql/hooks/ from .gitignore (now ignored alongside the rest of
  .pql/)
- !.pql/pql-plan.json from .gitignore (the legacy snapshot was
  deleted in the changelog migration; this un-ignore was already
  dead)
- The four tracked hook files (git rm --cached); local copies stay
  on disk and continue working.

Co-Authored-By: Claude <noreply@anthropic.com>

.pql/hooks/post-checkout

@@ -1,11 +0,0 @@
-#!/bin/sh
-# --- pql plan rebuild (post-checkout) ---
-# Auto-installed by pql init. On branch checkout (third arg == 1),
-# rebuild pql.db from the changelog so the local cache reflects the
-# new branch's planning state. File-level checkouts ($3 == 0) are
-# skipped.
-if [ "$3" = "1" ]; then
-    echo "pql: rebuilding planning database from changelog..." >&2
-    pql plan rebuild >/dev/null 2>&1 || true
-fi
-# --- end pql ---

.pql/hooks/post-merge

@@ -1,10 +0,0 @@
-#!/bin/sh
-# --- pql plan import ---
-# Auto-installed by pql init. Replays new changelog files into
-# pql.db, then re-syncs decisions from decisions/*.md so the
-# markdown-sourced half stays in step with whatever the merge
-# brought in. Both ops are idempotent — a no-op merge is a no-op
-# hook (D-8, D-16).
-pql plan import 2>/dev/null || true
-pql decisions sync 2>/dev/null || true
-# --- end pql ---

.pql/hooks/post-rewrite

@@ -1,8 +0,0 @@
-#!/bin/sh
-# --- pql plan rebuild (post-rewrite) ---
-# Auto-installed by pql init. Fires after rebase / amend, both of
-# which can rewrite the local view of the changelog. Rebuild is
-# safe and deterministic; incremental replay would miss removals.
-echo "pql: rebuilding planning database after rewrite..." >&2
-pql plan rebuild >/dev/null 2>&1 || true
-# --- end pql ---

.pql/hooks/pre-commit

@@ -1,8 +0,0 @@
-#!/bin/sh
-# --- pql plan export ---
-# Auto-installed by pql init. Exports planning state and stages the
-# snapshot so it lands in the same commit as the change that produced
-# it. The absolute pql path is baked in at install time — re-run
-# 'pql init' if the binary moves.
-pql plan export --stage 2>/dev/null || true
-# --- end pql ---