Add post-merge hook to auto-install dependencies (#7248)

* [AI] Add post-merge hook to auto-install when yarn.lock changes

Mirrors the existing post-checkout hook behavior: after a git pull or
merge, if yarn.lock changed between ORIG_HEAD and HEAD, automatically
runs yarn install to keep dependencies in sync.

https://claude.ai/code/session_01JHoMhGANLTc1q67s1dUHrt

* Add release notes for PR #7248

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

.husky/post-merge

@@ -0,0 +1,7 @@
+#!/bin/sh
+# Run yarn install after pulling/merging (if yarn.lock changed)
+
+if git diff --name-only ORIG_HEAD HEAD | grep -q "^yarn.lock$"; then
+  echo "yarn.lock changed — running yarn install..."
+  yarn install
+fi

upcoming-release-notes/7248.md

@@ -0,0 +1,6 @@
+---
+category: Maintenance
+authors: [MatissJanis]
+---
+
+Add post-merge hook to automatically install dependencies when yarn.lock changes after merges.