Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/scripts/upgradeable/patch-save.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+DIRNAME="$(dirname -- "${BASH_SOURCE[0]}")"
+PATCH="$DIRNAME/upgradeable.patch"
+
+error() {
+  echo Error: "$*" >&2
+  exit 1
+}
+
+if ! git diff-files --quiet ":!$PATCH"; then
+  error "Unstaged changes. Stage to include in patch or temporarily stash."
+fi
+
+git diff-index --cached --patch --output="$PATCH" HEAD
+git restore --staged --worktree ":!$PATCH"