feat: redesign Exams List page to show submitted custom exams

- Added Custom Exams tab showing all exams from Generation page
- Displays title, module badges, duration, and status
- Added Create Exam button
- Kept Exam Sessions tab for institutional sessions
- Search filters across exams

Made-with: Cursor

node_modules/dom-helpers/esm/isWindow.js

@@ -0,0 +1,6 @@
+import isDocument from './isDocument';
+export default function isWindow(node) {
+  if ('window' in node && node.window === node) return node;
+  if (isDocument(node)) return node.defaultView || false;
+  return false;
+}