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/error.tsx

@@ -0,0 +1,46 @@
+"use client";
+
+import { useEffect } from "react";
+import { Button } from "@/components/ui/button";
+import { AlertTriangle, RefreshCw, Home } from "lucide-react";
+import Link from "next/link";
+
+export default function Error({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  useEffect(() => {
+    console.error(error);
+  }, [error]);
+
+  return (
+    <div className="min-h-screen flex flex-col items-center justify-center bg-zinc-50 dark:bg-zinc-950 px-4">
+      <div className="text-center space-y-6 max-w-md">
+        <div className="flex justify-center">
+          <div className="bg-orange-100 dark:bg-orange-900/30 p-4 rounded-full">
+            <AlertTriangle className="h-12 w-12 text-orange-600 dark:text-orange-400" />
+          </div>
+        </div>
+        <h1 className="text-4xl font-bold tracking-tight">Oups ! Une erreur est survenue</h1>
+        <p className="text-muted-foreground text-lg">
+          La chèvre a glissé sur une peau de banane. Nous essayons de la remettre sur pied.
+        </p>
+        <div className="flex flex-col sm:flex-row gap-3 justify-center">
+          <Button onClick={reset} size="lg" className="gap-2">
+            <RefreshCw className="h-4 w-4" />
+            Réessayer
+          </Button>
+          <Button asChild variant="outline" size="lg" className="gap-2">
+            <Link href="/">
+              <Home className="h-4 w-4" />
+              Retourner à l'accueil
+            </Link>
+          </Button>
+        </div>
+      </div>
+    </div>
+  );
+}