Herstel potlood-icoon voor de aanpassen-knop bij slug

Consistent met de confirm/cancel-knoppen ernaast (ghost icon buttons)
in plaats van de tekst-linkknop.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/features/offerings/components/OfferingForm.tsx

@@ -2,7 +2,7 @@ import { useState } from 'react';
 import { useForm, useWatch } from 'react-hook-form';
 import { zodResolver } from '@hookform/resolvers/zod';
 import { useTranslation } from 'react-i18next';
-import { Check, Plus, Trash2, X } from 'lucide-react';
+import { Check, Pencil, Plus, Trash2, X } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
@@ -133,13 +133,13 @@ export function OfferingForm({ initialValues, onSubmit, isSubmitting }: Offering
                         </code>
                         <Button
                             type="button"
-                            variant="link"
+                            variant="ghost"
-                            size="sm"
+                            size="icon"
-                            className="h-auto p-0"
                             data-testid="offering-slug-edit"
+                            aria-label={t('offerings.form.editSlugButton')}
                             onClick={() => setIsEditingSlug(true)}
                         >
-                            {t('offerings.form.editSlugButton')}
+                            <Pencil className="size-4" />
                         </Button>
                     </div>
                 )}