feat: add Header and UserNav components, update layout to include Header and enhance profile page with settings link

thoughts-frontend/app/layout.tsx

@@ -3,6 +3,7 @@ import { Geist, Geist_Mono } from "next/font/google";
 import "./globals.css";
 import { AuthProvider } from "@/hooks/use-auth";
 import { Toaster } from "@/components/ui/sonner";
+import { Header } from "@/components/header";
 
 const geistSans = Geist({
   variable: "--font-geist-sans",
@@ -30,7 +31,8 @@ export default function RootLayout({
         className={`${geistSans.variable} ${geistMono.variable} antialiased`}
       >
         <AuthProvider>
-          {children}
+          <Header />
+          <main className="flex-1">{children}</main>
           <Toaster />
         </AuthProvider>
       </body>