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/app/(dashboard)/layout.tsx

@@ -0,0 +1,72 @@
+import { createClient } from '@/lib/supabase/server'
+import { redirect } from 'next/navigation'
+import { UserNav } from '@/components/layout/user-nav'
+import Link from 'next/link'
+
+export default async function DashboardLayout({
+  children,
+}: {
+  children: React.ReactNode
+}) {
+  const supabase = await createClient()
+
+  // Get user (should always exist due to middleware)
+  const { data: { user }, error: authError } = await supabase.auth.getUser()
+
+  if (authError || !user) {
+    redirect('/login')
+  }
+
+  // Get profile with plan info
+  const { data: profile } = await supabase
+    .from('profiles')
+    .select(`
+      *,
+      plans (
+        name,
+        display_name_it
+      )
+    `)
+    .eq('id', user.id)
+    .single()
+
+  return (
+    <div className="min-h-screen bg-gray-50">
+      {/* Header */}
+      <header className="bg-white border-b border-gray-200">
+        <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
+          <div className="flex justify-between items-center h-16">
+            <div className="flex items-center gap-8">
+              <Link href="/dashboard" className="text-xl font-bold text-blue-600">
+                Leopost
+              </Link>
+              <nav className="hidden md:flex items-center gap-4">
+                <Link
+                  href="/dashboard"
+                  className="text-gray-600 hover:text-gray-900 text-sm font-medium"
+                >
+                  Dashboard
+                </Link>
+                <Link
+                  href="/subscription"
+                  className="text-gray-600 hover:text-gray-900 text-sm font-medium"
+                >
+                  Piano
+                </Link>
+              </nav>
+            </div>
+            <UserNav
+              email={user.email || ''}
+              planName={profile?.plans?.display_name_it}
+            />
+          </div>
+        </div>
+      </header>
+
+      {/* Main content */}
+      <main className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-8">
+        {children}
+      </main>
+    </div>
+  )
+}