install pql 1.4.26 changelog-mode hooks

Replaces the legacy pql-plan.json export hooks with the new
changelog-aware set: pre-commit now stages incremental changelog
deltas via 'pql plan export --stage'; post-merge replays new
changelog files into pql.db; post-checkout / post-rewrite rebuild
pql.db when branch state changes. Companion shims under .githooks/
keep core.hooksPath = .githooks the single activation point.

Hook bodies are de-baked — pql 1.4.26 ships them with absolute
paths to the local pql binary, which doesn't survive cross-machine
tracking. Restored 'pql' on PATH form so the tracked copy stays
portable. Filed back-channel for pql to keep portable form.

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

.githooks/post-checkout

@@ -0,0 +1,3 @@
+#!/bin/sh
+# pql: source .pql/hooks/post-checkout (rebuild pql.db on branch checkout)
+. "$(git rev-parse --show-toplevel)/.pql/hooks/post-checkout"

.githooks/post-rewrite

@@ -0,0 +1,3 @@
+#!/bin/sh
+# pql: source .pql/hooks/post-rewrite (rebuild pql.db after rebase / amend)
+. "$(git rev-parse --show-toplevel)/.pql/hooks/post-rewrite"