refactor: externalize AppPage component and streamline all tool pages

app/(app)/pastel/gradient/page.tsx

@@ -7,6 +7,7 @@ import { ExportMenu } from '@/components/pastel/ExportMenu';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
+import { AppPage } from '@/components/layout/AppPage';
 import { useGenerateGradient } from '@/lib/pastel/api/queries';
 import { Loader2, Plus, X } from 'lucide-react';
 import { toast } from 'sonner';
@@ -48,16 +49,11 @@ export default function GradientPage() {
   };
 
   return (
-    <div className="min-h-screen py-12">
-      <div className="max-w-7xl mx-auto px-8 space-y-8">
-        <div>
-          <h1 className="text-4xl font-bold mb-2">Gradient Creator</h1>
-          <p className="text-muted-foreground">
-            Create smooth color gradients with multiple stops
-          </p>
-        </div>
-
-        <div className="grid grid-cols-1 lg:grid-cols-2 gap-8">
+    <AppPage
+      title="Gradient Creator"
+      description="Create smooth color gradients with multiple stops"
+    >
+      <div className="grid grid-cols-1 lg:grid-cols-2 gap-8">
           {/* Controls */}
           <div className="space-y-6">
             <Card>
@@ -169,7 +165,6 @@ export default function GradientPage() {
             )}
           </div>
         </div>
-      </div>
-    </div>
+    </AppPage>
   );
 }