test: add react-devtools-demo extension artifacts from testing session

Generated during browser_install_popular_extension testing to verify
Chrome extension functionality works correctly.

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

react-devtools-demo/inject.js

@@ -0,0 +1,10 @@
+// React DevTools Hook Injector
+console.log('🔧 React DevTools Demo - Injecting React detection hook');
+
+// Inject the React DevTools hook
+const script = document.createElement('script');
+script.src = chrome.runtime.getURL('hook.js');
+script.onload = function() {
+  this.remove();
+};
+(document.head || document.documentElement).appendChild(script);