Add Quiz feature: 10-question quizzes with progressive scoring (max 40 pts)

- Quizzes table with questions, answer options, attempts, answers
- Question types: multiple_choice, exclusion, true_false, free_text
- Progressive scoring: [1,1,2,2,3,3,4,6,8,10] = max 40 per quiz
- Alpine.js countdown timer per question with auto-submit on timeout
- Admin: CRUD for quizzes + per-question editor, JSON export/import
- Child: quiz overview with best scores, question view, result breakdown
- Nav: Quiz link in child header and admin sidebar

resources/views/layouts/child.blade.php

@@ -13,6 +13,7 @@
     </a>
     <div class="flex items-center gap-4">
       <a href="{{ route('learn.subjects') }}" class="text-sm font-medium text-slate-600 hover:text-indigo-600">Lernen</a>
+      <a href="{{ route('quiz.index') }}" class="text-sm font-medium text-slate-600 hover:text-indigo-600">🧠 Quiz</a>
       <a href="{{ route('rewards.index') }}" class="text-sm font-medium text-slate-600 hover:text-indigo-600">🪙 Belohnungen</a>
       <a href="{{ route('reference.index') }}" class="text-sm font-medium text-slate-600 hover:text-indigo-600">💡 Erinnerung</a>
       <div class="flex items-center gap-1 bg-amber-100 text-amber-700 font-bold rounded-full px-3 py-1 text-sm">