feat(domaincheck): support all TLDs with suggestion alternatives

- Accept full domains (e.g. "example.xyz") not just labels
- Check the entered TLD as primary result
- Show .de, .com, .net, .org as alternative suggestions below
- Primary result highlighted with accent border
- Input without TLD still works (shows all 4 suggestions)
- Updated i18n placeholders and added "suggestions" label

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/messages/de.json

@@ -221,7 +221,8 @@
   "domaincheck": {
     "title": "Domaincheck",
     "description": "Pruefe ob eine Domain verfuegbar ist",
-    "inputPlaceholder": "Domain eingeben (z.B. beispiel)",
+    "inputPlaceholder": "Domain eingeben (z.B. beispiel.de)",
+    "suggestions": "Alternativen",
     "checkButton": "Pruefen",
     "statusAvailable": "Verfuegbar",
     "statusRegistered": "Registriert",