feat: bug fixes, layout improvements, and new features

Bug fixes:
- Remove non-existent `role` column from admin users SQL query (A1)
- Fix Nextcloud Talk chat API path v4 → v1 for messages/send/read (A2)
- Fix ServiceModeTab sync: useState → useEffect to reflect DB state (A3)
- Guard BookStack book_slug with book_id fallback to avoid broken URLs (A4)

Layout & UI:
- Chat panel: sticky full-height positioning, main content scrolls independently (B1)
- Vehicle booking datetime inputs: explicit text color for dark mode (B2)
- AnnouncementBanner moved into grid with full-width span (B3)

Features:
- Per-user widget visibility preferences stored in users.preferences JSONB (C1)
- Link collections: grouped external links in admin UI and dashboard widget (C2)
- Admin ping history: migration 026, checked_at timestamps, expandable history rows (C4)
- Service mode end date picker with scheduled deactivation display (C5)
- Vikunja startup config logging and configured:false warnings (C7)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Dashboard.tsx

@@ -4,6 +4,7 @@ import {
   Box,
   Fade,
 } from '@mui/material';
+import { useQuery } from '@tanstack/react-query';
 import { useAuth } from '../contexts/AuthContext';
 import DashboardLayout from '../components/dashboard/DashboardLayout';
 import SkeletonCard from '../components/shared/SkeletonCard';
@@ -22,6 +23,10 @@ import AdminStatusWidget from '../components/dashboard/AdminStatusWidget';
 import AnnouncementBanner from '../components/dashboard/AnnouncementBanner';
 import VehicleBookingQuickAddWidget from '../components/dashboard/VehicleBookingQuickAddWidget';
 import EventQuickAddWidget from '../components/dashboard/EventQuickAddWidget';
+import LinksWidget from '../components/dashboard/LinksWidget';
+import { preferencesApi } from '../services/settings';
+import { WidgetKey } from '../constants/widgets';
+
 function Dashboard() {
   const { user } = useAuth();
   const isAdmin = user?.groups?.includes('dashboard_admin') ?? false;
@@ -33,6 +38,15 @@ function Dashboard() {
   ) ?? false;
   const [dataLoading, setDataLoading] = useState(true);
 
+  const { data: preferences } = useQuery({
+    queryKey: ['user-preferences'],
+    queryFn: preferencesApi.get,
+  });
+
+  const widgetVisible = (key: WidgetKey) => {
+    return preferences?.widgets?.[key] !== false;
+  };
+
   useEffect(() => {
     const timer = setTimeout(() => {
       setDataLoading(false);
@@ -44,7 +58,6 @@ function Dashboard() {
   return (
     <DashboardLayout>
       <Container maxWidth={false} disableGutters>
-        <AnnouncementBanner />
         <Box
           sx={{
             display: 'grid',
@@ -53,6 +66,9 @@ function Dashboard() {
             alignItems: 'start',
           }}
         >
+          {/* Announcement Banner — spans full width, renders null when no banners */}
+          <AnnouncementBanner gridColumn="1 / -1" />
+
           {/* User Profile Card — full width, contains welcome greeting */}
           {user && (
             <Box sx={{ gridColumn: '1 / -1' }}>
@@ -69,6 +85,7 @@ function Dashboard() {
           )}
 
           {/* Vehicle Status Card */}
+          {widgetVisible('vehicles') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '300ms' }}>
               <Box>
@@ -76,8 +93,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Equipment Status Card */}
+          {widgetVisible('equipment') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '350ms' }}>
               <Box>
@@ -85,9 +104,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Atemschutz Status Card */}
-          {canViewAtemschutz && (
+          {canViewAtemschutz && widgetVisible('atemschutz') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '400ms' }}>
               <Box>
@@ -98,6 +118,7 @@ function Dashboard() {
           )}
 
           {/* Upcoming Events Widget */}
+          {widgetVisible('events') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '440ms' }}>
               <Box>
@@ -105,8 +126,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Nextcloud Talk Widget */}
+          {widgetVisible('nextcloudTalk') && (
           <Box>
             {dataLoading ? (
               <SkeletonCard variant="basic" />
@@ -118,8 +141,10 @@ function Dashboard() {
               </Fade>
             )}
           </Box>
+          )}
 
           {/* BookStack Recent Pages Widget */}
+          {widgetVisible('bookstackRecent') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '520ms' }}>
               <Box>
@@ -127,8 +152,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* BookStack Search Widget */}
+          {widgetVisible('bookstackSearch') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '560ms' }}>
               <Box>
@@ -136,8 +163,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Vikunja — My Tasks Widget */}
+          {widgetVisible('vikunjaTasks') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '600ms' }}>
               <Box>
@@ -145,8 +174,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Vikunja — Quick Add Widget */}
+          {widgetVisible('vikunjaQuickAdd') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '640ms' }}>
               <Box>
@@ -154,9 +185,10 @@ function Dashboard() {
               </Box>
             </Fade>
           </Box>
+          )}
 
           {/* Vehicle Booking — Quick Add Widget */}
-          {canWrite && (
+          {canWrite && widgetVisible('vehicleBooking') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '720ms' }}>
               <Box>
@@ -167,7 +199,7 @@ function Dashboard() {
           )}
 
           {/* Event — Quick Add Widget */}
-          {canWrite && (
+          {canWrite && widgetVisible('eventQuickAdd') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '760ms' }}>
               <Box>
@@ -180,8 +212,19 @@ function Dashboard() {
           {/* Vikunja — Overdue Notifier (invisible, polling component) */}
           <VikunjaOverdueNotifier />
 
+          {/* Links Widget */}
+          {widgetVisible('links') && (
+          <Box>
+            <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '790ms' }}>
+              <Box>
+                <LinksWidget />
+              </Box>
+            </Fade>
+          </Box>
+          )}
+
           {/* Admin Status Widget — only for admins */}
-          {isAdmin && (
+          {isAdmin && widgetVisible('adminStatus') && (
           <Box>
             <Fade in={!dataLoading} timeout={600} style={{ transitionDelay: '680ms' }}>
               <Box>