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/(dashboard)/layout.tsx

@@ -0,0 +1,33 @@
+import * as React from "react";
+import { SidebarProvider, SidebarTrigger, SidebarInset } from "@/components/ui/sidebar";
+import { AppSidebar } from "@/components/app-sidebar";
+import { SearchSidebar } from "@/components/search-sidebar";
+import { MobileFilters } from "@/components/mobile-filters";
+
+export default function DashboardLayout({
+  children,
+  modal,
+}: {
+  children: React.ReactNode;
+  modal: React.ReactNode;
+}) {
+  return (
+    <SidebarProvider>
+      <AppSidebar />
+      <SidebarInset className="flex flex-row overflow-hidden">
+        <div className="flex-1 flex flex-col min-w-0">
+          <header className="flex h-16 shrink-0 items-center gap-2 border-b px-4 lg:hidden">
+            <SidebarTrigger />
+            <div className="flex-1" />
+          </header>
+          <main className="flex-1 overflow-y-auto bg-zinc-50 dark:bg-zinc-950">
+            {children}
+            {modal}
+          </main>
+          <MobileFilters />
+        </div>
+        <SearchSidebar />
+      </SidebarInset>
+    </SidebarProvider>
+  );
+}