feat(notfound): add NotFound page with 404 handling and localization

src/i18n/en.json

@@ -588,5 +588,11 @@
       "note": "The event has been automatically removed from your calendar.",
       "footer": "This message was sent automatically by {appName}."
     }
+  },
+  "notFound": {
+    "title": "Page not found",
+    "description": "The page you are looking for doesn't exist or has been moved.",
+    "goBack": "Go back",
+    "goHome": "Back to home"
   }
 }