feat(01-05): add protected dashboard layout and page

- Create UserNav component with logout functionality
- Add dashboard layout with header, navigation, and user info
- Create dashboard page displaying plan info and onboarding steps
- All text in Italian for target audience

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/layout/user-nav.tsx

@@ -0,0 +1,43 @@
+'use client'
+
+import { createClient } from '@/lib/supabase/client'
+import { useRouter } from 'next/navigation'
+import { Button } from '@/components/ui/button'
+import { useState } from 'react'
+
+interface UserNavProps {
+  email: string
+  planName?: string
+}
+
+export function UserNav({ email, planName }: UserNavProps) {
+  const [loading, setLoading] = useState(false)
+  const router = useRouter()
+  const supabase = createClient()
+
+  async function handleSignOut() {
+    setLoading(true)
+    await supabase.auth.signOut()
+    router.push('/login')
+    router.refresh()
+  }
+
+  return (
+    <div className="flex items-center gap-4">
+      <div className="text-sm text-right">
+        <p className="font-medium">{email}</p>
+        {planName && (
+          <p className="text-gray-500 text-xs capitalize">Piano {planName}</p>
+        )}
+      </div>
+      <Button
+        variant="outline"
+        size="sm"
+        onClick={handleSignOut}
+        disabled={loading}
+      >
+        {loading ? 'Uscita...' : 'Esci'}
+      </Button>
+    </div>
+  )
+}