fix(onboarding): move LanguageSwitcher out of absolute positioning to avoid mobile overlap

Absolutely positioning it at top-4 right-4 over the centered content
overlapped the step headings on narrow viewports (reported live).
Gives it its own row in a flex-col layout instead, so it never
competes for space with the card content below it.

src/app/onboarding/pet/page.tsx

@@ -83,11 +83,13 @@ export default function OnboardingPetPage() {
   }
 
   return (
-    <main className="relative min-h-screen flex items-center justify-center bg-background px-4">
-      <div className="absolute top-4 right-4">
+    <main className="min-h-screen flex flex-col bg-background">
+      <div className="flex justify-end p-4">
         <LanguageSwitcher />
       </div>
-      {content}
+      <div className="flex-1 flex items-center justify-center px-4 pb-8">
+        {content}
+      </div>
     </main>
   );
 }