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

app/Models/QuizQuestion.php

@@ -0,0 +1,17 @@
+<?php
+namespace App\Models;
+use Illuminate\Database\Eloquent\Model;
+class QuizQuestion extends Model {
+    protected $fillable = ['quiz_id','sort_order','type','question_text','time_limit','correct_answer'];
+    public function quiz()          { return $this->belongsTo(Quiz::class); }
+    public function answerOptions() { return $this->hasMany(QuizAnswerOption::class,'quiz_question_id')->orderBy('sort_order'); }
+    public function typeLabel(): string {
+        return match($this->type) {
+            'multiple_choice' => 'Multiple Choice',
+            'exclusion'       => 'Ausschluss',
+            'true_false'      => 'Wahr/Falsch',
+            'free_text'       => 'Freitext',
+            default           => $this->type,
+        };
+    }
+}