feat(leaderboard): add leaderboard functionaltiy

src/utils/api.ts

@@ -1,3 +1,4 @@
+import type { Leaderboard } from "../types/leaderboard";
 import type { Lesson, LessonsResponse } from "../types/lesson";
 import type {
   SessionAnswerResponse,
@@ -222,5 +223,9 @@ class ApiClient {
   async fetchTopicById(token: string, topicId: string): Promise<Topic> {
     return this.authenticatedRequest<Topic>(`/topics/${topicId}`, token);
   }
+
+  async fetchLeaderboard(token: string): Promise<Leaderboard> {
+    return this.authenticatedRequest<Leaderboard>(`/leaderboard/`, token);
+  }
 }
 export const api = new ApiClient(API_URL);