frontend: refactor preview

frontend/src/appShellContext.js

@@ -0,0 +1,12 @@
+import React from 'react';
+
+export const AppShellContext = React.createContext(null);
+
+export const useAppShell = () => {
+  const context = React.useContext(AppShellContext);
+  if (!context) {
+    throw new Error('AppShellContext not found. Ensure routes are nested under AppLayout.');
+  }
+  return context;
+};
+