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/date-fns/_lib/defaultOptions.mjs

@@ -0,0 +1,9 @@
+let defaultOptions = {};
+
+export function getDefaultOptions() {
+  return defaultOptions;
+}
+
+export function setDefaultOptions(newOptions) {
+  defaultOptions = newOptions;
+}