refactor: extract dashboard layout under /(dashboard)

ee/tabby-ui/app/(dashboard)/layout.tsx

@@ -1,5 +1,6 @@
 import { Metadata } from 'next'
 import Sidebar from './components/sidebar'
+import { Header } from '@/components/header'
 
 export const metadata: Metadata = {
   title: 'Dashboard'
@@ -10,5 +11,10 @@ interface DashboardLayoutProps {
 }
 
 export default function RootLayout({ children }: DashboardLayoutProps) {
-  return <Sidebar className="flex-1">{children}</Sidebar>
+  return <>
+    <Header />
+    <main className="bg-muted/50 flex flex-1 flex-col">
+      <Sidebar className="flex-1">{children}</Sidebar>
+    </main>
+  </>
 }

ee/tabby-ui/app/layout.tsx

@@ -39,8 +39,7 @@ export default function RootLayout({ children }: RootLayoutProps) {
         <Toaster />
         <Providers attribute="class" defaultTheme="system" enableSystem>
           <div className="flex min-h-screen flex-col">
-            <Header />
+            {children}
-            <main className="bg-muted/50 flex flex-1 flex-col">{children}</main>
           </div>
           <TailwindIndicator />
         </Providers>