resolve issues with new features

frontend/src/pages/AdminDashboard.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect } from 'react';
 import { Box, Tabs, Tab, Typography } from '@mui/material';
-import { Navigate, useSearchParams } from 'react-router-dom';
+import { Navigate, useNavigate, useSearchParams } from 'react-router-dom';
 import DashboardLayout from '../components/dashboard/DashboardLayout';
 import ServiceManagerTab from '../components/admin/ServiceManagerTab';
 import SystemHealthTab from '../components/admin/SystemHealthTab';
@@ -24,6 +24,7 @@ function TabPanel({ children, value, index }: TabPanelProps) {
 const ADMIN_TAB_COUNT = 6;
 
 function AdminDashboard() {
+  const navigate = useNavigate();
   const [searchParams] = useSearchParams();
   const [tab, setTab] = useState(() => {
     const t = Number(searchParams.get('tab'));
@@ -47,7 +48,7 @@ function AdminDashboard() {
       <Typography variant="h4" sx={{ mb: 3 }}>Administration</Typography>
 
       <Box sx={{ borderBottom: 1, borderColor: 'divider' }}>
-        <Tabs value={tab} onChange={(_e, v) => setTab(v)}>
+        <Tabs value={tab} onChange={(_e, v) => { setTab(v); navigate(`/admin?tab=${v}`, { replace: true }); }}>
           <Tab label="Services" />
           <Tab label="System" />
           <Tab label="Benutzer" />

frontend/src/pages/AusruestungDetail.tsx

@@ -159,8 +159,8 @@ const UebersichtTab: React.FC<UebersichtTabProps> = ({ equipment, onStatusUpdate
       await equipmentApi.updateStatus(equipment.id, payload);
       setStatusDialogOpen(false);
       onStatusUpdated();
-    } catch {
-      setSaveError('Status konnte nicht gespeichert werden.');
+    } catch (err: any) {
+      setSaveError(err?.response?.data?.message || 'Status konnte nicht gespeichert werden.');
     } finally {
       setSaving(false);
     }

frontend/src/pages/FahrzeugDetail.tsx

@@ -153,8 +153,8 @@ const UebersichtTab: React.FC<UebersichtTabProps> = ({ vehicle, onStatusUpdated,
       await vehiclesApi.updateStatus(vehicle.id, payload);
       setStatusDialogOpen(false);
       onStatusUpdated();
-    } catch {
-      setSaveError('Status konnte nicht gespeichert werden.');
+    } catch (err: any) {
+      setSaveError(err?.response?.data?.message || 'Status konnte nicht gespeichert werden.');
     } finally {
       setSaving(false);
     }

frontend/src/pages/Kalender.tsx

@@ -2158,7 +2158,7 @@ export default function Kalender() {
         {/* Tabs */}
         <Tabs
           value={activeTab}
-          onChange={(_, v) => setActiveTab(v)}
+          onChange={(_, v) => { setActiveTab(v); navigate(`/kalender?tab=${v}`, { replace: true }); }}
           sx={{ mb: 2, borderBottom: 1, borderColor: 'divider' }}
         >
           <Tab icon={<EventIcon />} iconPosition="start" label="Dienste & Veranstaltungen" />