chore(js): add react-grab to clerk-js sandbox

Loads react-grab from unpkg in the sandbox template so component
locations can be inspected during local development. The sandbox has
no production build, so the script is intrinsically dev-only.

Author: kylemac

.changeset/old-months-grow.md

@@ -0,0 +1,2 @@
+---
+---

packages/clerk-js/package.json

@@ -114,6 +114,7 @@
     "bundlewatch": "^0.4.2",
     "jsdom": "26.1.0",
     "minimatch": "^10.2.5",
+    "react-grab": "^0.1.37",
     "webpack-merge": "^5.10.0"
   },
   "engines": {

packages/clerk-js/sandbox/template.html

@@ -36,6 +36,11 @@
         }
       })();
     </script>
+    <!-- React Grab (development-only: this template is only used by `pnpm dev:sandbox`) -->
+    <script
+      src="//unpkg.com/react-grab/dist/index.global.js"
+      crossorigin="anonymous"
+    ></script>
     <script>
       class NavLink extends HTMLElement {
         connectedCallback() {