feat(api): add exam->challenge map and routes (#61683)

Co-authored-by: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

api/vitest.utils.ts

@@ -211,7 +211,8 @@ If you are seeing this error, the root cause is likely an error thrown in the be
   });
 }
 
-export const defaultUserId = '64c7810107dd4782d32baee7';
+// demoUser _id to allow testing with mock data
+export const defaultUserId = '5bd30e0f1caf6ac3ddddddb5';
 export const defaultUserEmail = 'foo@bar.com';
 export const defaultUsername = 'fcc-test-user';