fix(frontend): Use correct singular form for circle preview placeholder

Add circles.form.defaultName translation key for the preview placeholder
text instead of using circles.title (which is plural "Circles"/"Kreise").

Author: claude

apps/frontend/src/lib/components/circles/CircleEditModal.svelte

@@ -276,7 +276,7 @@ function handleBackdropClick(e: MouseEvent) {
           <span class="block text-sm font-body font-semibold text-gray-700 mb-2">
             {$i18n.t('circles.form.preview')}
           </span>
-          <CircleChip circle={{ id: 'preview', name: formName || $i18n.t('circles.title'), color: formColor }} size="md" />
+          <CircleChip circle={{ id: 'preview', name: formName || $i18n.t('circles.form.defaultName'), color: formColor }} size="md" />
         </div>
 
         <!-- Error message -->

apps/frontend/src/lib/i18n/locales/de.json

@@ -248,6 +248,7 @@
         "edit": "Kreis bearbeiten"
       },
       "name": "Name",
+      "defaultName": "Kreisname",
       "namePlaceholder": "z.B. Familie, Arbeit, Schule",
       "description": "Beschreibung",
       "descriptionPlaceholder": "Wofür ist dieser Kreis?",

apps/frontend/src/lib/i18n/locales/en.json

@@ -248,6 +248,7 @@
         "edit": "Edit Circle"
       },
       "name": "Name",
+      "defaultName": "Circle Name",
       "namePlaceholder": "e.g., Family, Work, School",
       "description": "Description",
       "descriptionPlaceholder": "What is this circle for?",