feat: Add custom 404 not found page

frontend/src/components/NotFound.tsx

@@ -0,0 +1,17 @@
+import { Typography } from "@mui/joy";
+import { useTranslation } from "react-i18next";
+
+export const NotFound = () => {
+  const { t } = useTranslation();
+
+  return (
+    <div className={"flex flex-col items-center gap-2"}>
+      <Typography color={"primary"} level={"h1"}>
+        {t("not-found-header")}
+      </Typography>
+      <Typography className={"text-slate-900"} level={"body-lg"}>
+        {t("not-found-body")}
+      </Typography>
+    </div>
+  );
+};

frontend/src/utils/i18n/locales/de/de.json

@@ -58,6 +58,8 @@
   "success": "Erfolg",
   "submit": "Absenden",
   "logout-success-text": "Logout erfolgreich!",
+  "not-found-header": "404 - Nicht gefunden",
+  "not-found-body": "Die Seite nach der du gesucht hast, gibt es nicht.",
   "SU005": "Das Passwort wurde erfolgreich geändert!",
   "SE001": "Die Einstellungen wurden erfolgreich geändert!",
   "EG001": "Ein unerwarteter Fehler ist aufgetreten. Bitte versuchen Sie es später erneut.",

frontend/src/utils/i18n/locales/en/en.json

@@ -58,6 +58,8 @@
   "success": "Success",
   "submit": "Submit",
   "logout-success-text": "Logout successful!",
+  "not-found-header": "404 - Not found",
+  "not-found-body": "The page you were looking for, does not exist.",
   "SU005": "Your password is updated successfully!",
   "SE001": "The settings are updated successfully!",
   "EG001": "An unexpected error occurred. Please try again later.",