Add global providers for react-query, theming, and auth

Introduce a new Providers component to manage global contexts including react-query, theme switching, and authentication. Added necessary dependencies: `@tanstack/react-query-devtools` and `next-themes`, and configured default options for react-query.

frontend/src/providers/index.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import React from "react";
+import { QueryClientProvider, QueryClient } from "@tanstack/react-query";
+import { ReactQueryDevtools } from "@tanstack/react-query-devtools";
+import { AuthProvider } from "@/context/auth-context";
+import { ThemeProvider } from "next-themes";
+
+// Create a client
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      retry: 1,
+      refetchOnWindowFocus: false,
+      staleTime: 1000 * 60 * 5, // 5 minutes
+    },
+  },
+});
+
+export function Providers({ children }: { children: React.ReactNode }) {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <ThemeProvider
+        attribute="class"
+        defaultTheme="system"
+        enableSystem
+        disableTransitionOnChange
+      >
+        <AuthProvider>{children}</AuthProvider>
+      </ThemeProvider>
+      <ReactQueryDevtools initialIsOpen={false} />
+    </QueryClientProvider>
+  );
+}