refactor(frontend): ♻️ update API folder structure

frontend/api/admin-api.ts

@@ -0,0 +1,21 @@
+import { AdminAboutAPI } from "./admin/admin-about";
+import { AdminTaskAPI } from "./admin/admin-tasks";
+import { ApiRequestInstance } from "~/types/api";
+
+export class AdminAPI {
+  private static instance: AdminAPI;
+  public about: AdminAboutAPI;
+  public serverTasks: AdminTaskAPI;
+
+  constructor(requests: ApiRequestInstance) {
+    if (AdminAPI.instance instanceof AdminAPI) {
+      return AdminAPI.instance;
+    }
+
+    this.about = new AdminAboutAPI(requests);
+    this.serverTasks = new AdminTaskAPI(requests);
+
+    Object.freeze(this);
+    AdminAPI.instance = this;
+  }
+}