Add Erinnerung (reference) section with articles for Deutsch, Mathe, Englisch

- Migration, model, admin+child controllers, all views
- 17 seeded articles: Nomen, Verben, Adjektive, Zeitformen, Satzarten,
  Wortarten, Ganze Zahlen, Grundrechenarten, Einmaleins, Geometrie,
  Brüche, Zahlen/Farben/Wochentage/Sätze/Tiere auf Englisch
- CSS for .ref-content (h2/h3/p/ul/table + .beispiel/.tipp/.merke blocks)
- Child nav + admin sidebar links

app/Http/Controllers/Admin/ReferenceController.php

@@ -0,0 +1,48 @@
+<?php
+namespace App\Http\Controllers\Admin;
+use App\Http\Controllers\Controller;
+use App\Models\ReferenceArticle;
+use Illuminate\Http\Request;
+use Illuminate\Support\Str;
+class ReferenceController extends Controller {
+    public function index() {
+        $articles = ReferenceArticle::orderBy('category')->orderBy('sort_order')->get()->groupBy('category');
+        $categories = ReferenceArticle::categories();
+        return view('admin.reference.index', compact('articles','categories'));
+    }
+    public function create() {
+        $categories = ReferenceArticle::categories();
+        return view('admin.reference.create', compact('categories'));
+    }
+    public function store(Request $r) {
+        $r->validate(['title'=>'required|string|max:120','category'=>'required|in:deutsch,mathe,englisch','icon'=>'required|string|max:8','content'=>'required|string']);
+        ReferenceArticle::create([
+            'title'      => $r->title,
+            'slug'       => Str::slug($r->title).'-'.uniqid(),
+            'category'   => $r->category,
+            'icon'       => $r->icon,
+            'content'    => $r->content,
+            'sort_order' => (int)$r->sort_order,
+        ]);
+        return redirect()->route('admin.reference.index')->with('success','Artikel erstellt.');
+    }
+    public function edit(ReferenceArticle $reference) {
+        $categories = ReferenceArticle::categories();
+        return view('admin.reference.edit', compact('reference','categories'));
+    }
+    public function update(Request $r, ReferenceArticle $reference) {
+        $r->validate(['title'=>'required|string|max:120','category'=>'required|in:deutsch,mathe,englisch','icon'=>'required|string|max:8','content'=>'required|string']);
+        $reference->update([
+            'title'      => $r->title,
+            'category'   => $r->category,
+            'icon'       => $r->icon,
+            'content'    => $r->content,
+            'sort_order' => (int)$r->sort_order,
+        ]);
+        return redirect()->route('admin.reference.index')->with('success','Gespeichert.');
+    }
+    public function destroy(ReferenceArticle $reference) {
+        $reference->delete();
+        return redirect()->route('admin.reference.index')->with('success','Artikel gelöscht.');
+    }
+}

app/Http/Controllers/Child/ReferenceController.php

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+<?php
+namespace App\Http\Controllers\Child;
+use App\Http\Controllers\Controller;
+use App\Models\ReferenceArticle;
+class ReferenceController extends Controller {
+    public function index() {
+        $articles   = ReferenceArticle::orderBy('sort_order')->get()->groupBy('category');
+        $categories = ReferenceArticle::categories();
+        return view('child.reference.index', compact('articles','categories'));
+    }
+    public function show(ReferenceArticle $reference) {
+        $others = ReferenceArticle::where('category', $reference->category)
+            ->where('id','!=',$reference->id)->orderBy('sort_order')->get();
+        return view('child.reference.show', compact('reference','others'));
+    }
+}

app/Models/ReferenceArticle.php

@@ -0,0 +1,9 @@
+<?php
+namespace App\Models;
+use Illuminate\Database\Eloquent\Model;
+class ReferenceArticle extends Model {
+    protected $fillable = ['title','slug','category','icon','content','sort_order'];
+    public static function categories(): array {
+        return ['deutsch' => '📖 Deutsch', 'mathe' => '🔢 Mathe', 'englisch' => '🌍 Englisch'];
+    }
+}