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/app/robots.ts

@@ -0,0 +1,14 @@
+import type { MetadataRoute } from "next";
+
+export default function robots(): MetadataRoute.Robots {
+  const baseUrl = process.env.NEXT_PUBLIC_APP_URL || "https://memegoat.local";
+  
+  return {
+    rules: {
+      userAgent: "*",
+      allow: "/",
+      disallow: ["/settings/", "/upload/", "/api/"],
+    },
+    sitemap: `${baseUrl}/sitemap.xml`,
+  };
+}