Wire all 7 learn pages to central translation system

All exercise pages now use useNativeLanguage() hook:
- Buttons show text in user's native language (Richtig→Dogru, etc.)
- Instructions translated (Geschafft→Bitti, Nochmal→Tekrar, etc.)
- wordInNative() available for vocab translations (needs data)

Pages updated: flashcards, quiz, type, listen, match, pronounce, story.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

studio-v2/app/learn/[unitId]/quiz/page.tsx

@@ -3,6 +3,7 @@
 import React, { useState, useEffect, useCallback } from 'react'
 import { useParams, useRouter } from 'next/navigation'
 import { useTheme } from '@/lib/ThemeContext'
+import { useNativeLanguage } from '@/lib/useNativeLanguage'
 import { QuizQuestion } from '@/components/learn/QuizQuestion'
 
 interface MCQuestion {
@@ -21,6 +22,7 @@ export default function QuizPage() {
   const { unitId } = useParams<{ unitId: string }>()
   const router = useRouter()
   const { isDark } = useTheme()
+  const { t, wordInNative, nativeLang, isThirdLanguage } = useNativeLanguage()
 
   const [questions, setQuestions] = useState<MCQuestion[]>([])
   const [currentIndex, setCurrentIndex] = useState(0)
@@ -110,7 +112,7 @@ export default function QuizPage() {
               {stats.correct === questions.length ? '🏆' : stats.correct > stats.incorrect ? '🎉' : '💪'}
             </div>
             <h2 className={`text-2xl font-bold mb-2 ${isDark ? 'text-white' : 'text-slate-900'}`}>
-              {stats.correct === questions.length ? 'Perfekt!' : 'Geschafft!'}
+              {stats.correct === questions.length ? 'Perfekt!' : t('done')}
             </h2>
             <p className={`text-lg mb-4 ${isDark ? 'text-white/70' : 'text-slate-600'}`}>
               {stats.correct} von {questions.length} richtig