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/components/content-skeleton.tsx

@@ -0,0 +1,35 @@
+import { Card, CardContent, CardFooter, CardHeader } from "@/components/ui/card";
+import { Skeleton } from "@/components/ui/skeleton";
+
+export function ContentSkeleton() {
+  return (
+    <Card className="overflow-hidden border-none shadow-sm">
+      <CardHeader className="p-4 flex flex-row items-center space-y-0 gap-3">
+        <Skeleton className="h-8 w-8 rounded-full" />
+        <div className="flex flex-col gap-1.5">
+          <Skeleton className="h-3 w-24" />
+          <Skeleton className="h-2 w-16" />
+        </div>
+      </CardHeader>
+      <CardContent className="p-0 aspect-square">
+        <Skeleton className="h-full w-full" />
+      </CardContent>
+      <CardFooter className="p-4 flex flex-col gap-4">
+        <div className="w-full flex justify-between">
+          <div className="flex gap-2">
+            <Skeleton className="h-8 w-12 rounded-md" />
+            <Skeleton className="h-8 w-12 rounded-md" />
+          </div>
+          <Skeleton className="h-8 w-20 rounded-md" />
+        </div>
+        <div className="w-full space-y-2">
+          <Skeleton className="h-4 w-full" />
+          <div className="flex gap-1">
+            <Skeleton className="h-4 w-12" />
+            <Skeleton className="h-4 w-12" />
+          </div>
+        </div>
+      </CardFooter>
+    </Card>
+  );
+}