ajout plan byok, plus correction d'affichage et navigation

src/app/pricing/page.tsx

@@ -31,7 +31,7 @@ export default function PricingPage() {
             isLoading={isLoading}
             currentPlan={user?.subscription.plan || 'free'}
             onBack={() => router.push(user ? '/dashboard' : '/')}
-            onSelectPlan={() => router.push(user ? '/checkout' : '/login')}
+            onSelectPlan={(id) => router.push(user ? `/checkout?plan=${id}` : '/login')}
         />
     );
 }