feat: introduce new app routes with modular structure and enhanced features

Added modular app routes including `login`, `dashboard`, `categories`, `trends`, and `upload`. Introduced reusable components such as `ContentList`, `ContentSkeleton`, and `AppSidebar` for improved UI consistency. Enhanced authentication with `AuthProvider` and implemented lazy loading, dynamic layouts, and infinite scrolling for better performance.

frontend/src/lib/api.ts

@@ -0,0 +1,11 @@
+import axios from "axios";
+
+const api = axios.create({
+  baseURL: process.env.NEXT_PUBLIC_API_URL || "http://localhost:3000",
+  withCredentials: true,
+  headers: {
+    "Content-Type": "application/json",
+  },
+});
+
+export default api;