feat(fullstack): Add server health check with overlay

legalconsenthub/i18n/locales/en.json

@@ -5,5 +5,13 @@
     "employer": "Employer",
     "worksCouncilMember": "Works Council Member",
     "worksCouncilChair": "Works Council Chair"
+  },
+  "serverConnection": {
+    "title": "Server Connection Lost",
+    "message": "The connection to the server is currently unavailable. We are automatically trying to restore the connection.",
+    "checking": "Checking connection...",
+    "lastCheck": "Last check",
+    "retryInfo": "Automatic retry every 60 seconds",
+    "retryNow": "Try again now"
   }
 }