refactor: externalize AppPage component and streamline all tool pages

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

@@ -5,6 +5,7 @@ import { ColorPicker } from '@/components/pastel/ColorPicker';
 import { Button } from '@/components/ui/button';
 import { Badge } from '@/components/ui/badge';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
+import { AppPage } from '@/components/layout/AppPage';
 import { getContrastRatio, hexToRgb, checkWCAGCompliance } from '@/lib/pastel/utils/color';
 import { ArrowLeftRight, Check, X } from 'lucide-react';
 
@@ -57,16 +58,11 @@ export default function ContrastPage() {
   );
 
   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">Contrast Checker</h1>
-          <p className="text-muted-foreground">
-            Test color combinations for WCAG 2.1 compliance
-          </p>
-        </div>
-
-        <div className="grid grid-cols-1 lg:grid-cols-2 gap-8">
+    <AppPage
+      title="Contrast Checker"
+      description="Test color combinations for WCAG 2.1 compliance"
+    >
+      <div className="grid grid-cols-1 lg:grid-cols-2 gap-8">
           {/* Color Pickers */}
           <div className="space-y-6">
             <Card>
@@ -183,7 +179,6 @@ export default function ContrastPage() {
             )}
           </div>
         </div>
-      </div>
-    </div>
+    </AppPage>
   );
 }