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/react-style-singleton/dist/es5/index.d.ts

@@ -0,0 +1,3 @@
+export { styleSingleton } from './component';
+export { stylesheetSingleton } from './singleton';
+export { styleHookSingleton } from './hook';