resolve issues with new features

frontend/src/components/admin/ServiceManagerTab.tsx

@@ -17,29 +17,38 @@ import {
   IconButton,
   Typography,
   CircularProgress,
+  Select,
+  MenuItem,
+  FormControl,
+  InputLabel,
 } from '@mui/material';
 import DeleteIcon from '@mui/icons-material/Delete';
 import AddIcon from '@mui/icons-material/Add';
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { adminApi } from '../../services/admin';
+import { useNotification } from '../../contexts/NotificationContext';
 import type { PingResult } from '../../types/admin.types';
 
 function ServiceManagerTab() {
   const queryClient = useQueryClient();
+  const { showError } = useNotification();
   const [dialogOpen, setDialogOpen] = useState(false);
   const [newName, setNewName] = useState('');
   const [newUrl, setNewUrl] = useState('');
+  const [refreshInterval, setRefreshInterval] = useState(15000);
 
   const { data: services, isLoading: servicesLoading } = useQuery({
     queryKey: ['admin', 'services'],
     queryFn: adminApi.getServices,
-    refetchInterval: 15000,
+    refetchInterval: refreshInterval || false,
+    placeholderData: (previousData: any) => previousData,
   });
 
   const { data: pingResults, isLoading: pingLoading } = useQuery({
     queryKey: ['admin', 'services', 'ping'],
     queryFn: adminApi.pingAll,
-    refetchInterval: 15000,
+    refetchInterval: refreshInterval || false,
+    placeholderData: (previousData: any) => previousData,
   });
 
   const createMutation = useMutation({
@@ -50,6 +59,10 @@ function ServiceManagerTab() {
       setNewName('');
       setNewUrl('');
     },
+    onError: (error: any) => {
+      const message = error?.response?.data?.message || 'Service konnte nicht erstellt werden';
+      showError(message);
+    },
   });
 
   const deleteMutation = useMutation({
@@ -57,6 +70,9 @@ function ServiceManagerTab() {
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['admin', 'services'] });
     },
+    onError: () => {
+      showError('Service konnte nicht gelöscht werden');
+    },
   });
 
   const getPingForUrl = (url: string): PingResult | undefined => {
@@ -102,9 +118,25 @@ function ServiceManagerTab() {
     <Box>
       <Box sx={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', mb: 2 }}>
         <Typography variant="h6">Service Monitor</Typography>
-        <Button startIcon={<AddIcon />} variant="contained" onClick={() => setDialogOpen(true)}>
-          Service hinzufuegen
-        </Button>
+        <Box sx={{ display: 'flex', alignItems: 'center', gap: 2 }}>
+          <FormControl size="small" sx={{ minWidth: 160 }}>
+            <InputLabel>Aktualisierung</InputLabel>
+            <Select
+              value={refreshInterval}
+              label="Aktualisierung"
+              onChange={(e) => setRefreshInterval(Number(e.target.value))}
+            >
+              <MenuItem value={5000}>5 Sekunden</MenuItem>
+              <MenuItem value={15000}>15 Sekunden</MenuItem>
+              <MenuItem value={30000}>30 Sekunden</MenuItem>
+              <MenuItem value={60000}>60 Sekunden</MenuItem>
+              <MenuItem value={0}>Aus</MenuItem>
+            </Select>
+          </FormControl>
+          <Button startIcon={<AddIcon />} variant="contained" onClick={() => setDialogOpen(true)}>
+            Service hinzufuegen
+          </Button>
+        </Box>
       </Box>
 
       <TableContainer component={Paper}>
@@ -185,6 +217,7 @@ function ServiceManagerTab() {
             fullWidth
             value={newUrl}
             onChange={(e) => setNewUrl(e.target.value)}
+            helperText="Vollständige URL mit http:// oder https://"
           />
         </DialogContent>
         <DialogActions>

frontend/src/components/admin/SystemHealthTab.tsx

@@ -19,16 +19,27 @@ function formatBytes(bytes: number): string {
 }
 
 function SystemHealthTab() {
-  const { data: health, isLoading } = useQuery({
+  const { data: health, isLoading, isError } = useQuery({
     queryKey: ['admin', 'system', 'health'],
     queryFn: adminApi.getSystemHealth,
     refetchInterval: 30000,
   });
 
-  if (isLoading || !health) {
+  if (isLoading) {
     return <Box sx={{ display: 'flex', justifyContent: 'center', p: 4 }}><CircularProgress /></Box>;
   }
 
+  if (isError || !health) {
+    return (
+      <Box sx={{ p: 4, textAlign: 'center' }}>
+        <Typography color="error" gutterBottom>Systemdaten konnten nicht geladen werden.</Typography>
+        <Typography variant="body2" color="text.secondary">
+          Bitte versuchen Sie es später erneut.
+        </Typography>
+      </Box>
+    );
+  }
+
   const heapPercent = (health.memoryUsage.heapUsed / health.memoryUsage.heapTotal) * 100;
 
   return (

frontend/src/components/admin/UserOverviewTab.tsx

@@ -40,7 +40,7 @@ function UserOverviewTab() {
   const [sortKey, setSortKey] = useState<SortKey>('name');
   const [sortDir, setSortDir] = useState<SortDir>('asc');
 
-  const { data: users, isLoading } = useQuery({
+  const { data: users, isLoading, isError } = useQuery({
     queryKey: ['admin', 'users'],
     queryFn: adminApi.getUsers,
   });
@@ -82,6 +82,17 @@ function UserOverviewTab() {
     return <Box sx={{ display: 'flex', justifyContent: 'center', p: 4 }}><CircularProgress /></Box>;
   }
 
+  if (isError) {
+    return (
+      <Box sx={{ p: 4, textAlign: 'center' }}>
+        <Typography color="error" gutterBottom>Benutzerdaten konnten nicht geladen werden.</Typography>
+        <Typography variant="body2" color="text.secondary">
+          Bitte versuchen Sie es später erneut.
+        </Typography>
+      </Box>
+    );
+  }
+
   return (
     <Box>
       <Box sx={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', mb: 2 }}>