feat: dodaj scheduled_date na Task i kalendar widget

- Novo polje Task.scheduled_date (DateField, nullable, db_index) za planiranje
- Migracija 0009_task_scheduled_date
- Celery task notify_upcoming_tasks: dnevno u 08:00 šalje Pusher + email za sutrašnje zadatke
- TaskCalendarWidget: react-spring slide panel s lijeve strane, grid prikaz mjeseca, dot indikatori, klik otvara TaskServiceRecordsModal
- FleetDashboardShell: import + render kalendara, Planirano stupac u tablici zadataka
- TaskCreateModal + TaskServiceRecordsModal: scheduled_date input i prikaz
- Admin + serializer + views: scheduled_date filter i prikaz
- 47 backend testova prolaze (uključuje 8 novih za notify_upcoming_tasks)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/components/dashboard/FleetDashboardShell.jsx

@@ -6,6 +6,7 @@ import WorkOrderModal from './WorkOrderModal';
 import TaskCreateModal from './TaskCreateModal';
 import TaskServiceRecordsModal from './TaskServiceRecordsModal';
 import WorkOrderDetailModal from './WorkOrderDetailModal';
+import TaskCalendarWidget from './TaskCalendarWidget';
 import SyncLogPanel from './SyncLogPanel';
 import ServiceRecordForm from '../fleet/ServiceRecordForm';
 import ServicePhotoUpload from '../fleet/ServicePhotoUpload';
@@ -578,6 +579,7 @@ export default function FleetDashboardShell({ initialSection = 'dashboard', page
     const taskColumns = [
         { key: 'title', label: 'Radni zadatak', className: 'px-4 py-3' },
         { key: 'status', label: 'Status', className: 'px-4 py-3' },
+        { key: 'scheduledDate', label: 'Planirano', className: 'px-4 py-3' },
         { key: 'createdAt', label: 'Vrijeme izrade', className: 'px-4 py-3' },
         { key: 'vehicle', label: 'Dizalica', className: 'px-4 py-3' },
         { key: 'workOrder', label: 'Putni nalog', className: 'px-4 py-3' },
@@ -591,6 +593,12 @@ export default function FleetDashboardShell({ initialSection = 'dashboard', page
 
     return (
         <AnimatedPage className="min-h-screen">
+            {hasMounted && (
+                <TaskCalendarWidget
+                    tasks={tasks}
+                    onTaskClick={(task) => setSelectedTask(task)}
+                />
+            )}
             <main className="min-w-0">
                 <DashboardTopbar
                     activeSection={activeSection}
@@ -750,6 +758,15 @@ export default function FleetDashboardShell({ initialSection = 'dashboard', page
                                                 {getStatusLabel(task.status || '-')}
                                             </span>
                                         </td>
+                                        <td className="px-4 py-3">
+                                            {task.scheduled_date ? (
+                                                <span className="font-medium text-indigo-700">
+                                                    {formatDate(task.scheduled_date)}
+                                                </span>
+                                            ) : (
+                                                <span className="text-text-muted">-</span>
+                                            )}
+                                        </td>
                                         <td
                                             className="px-4 py-3"
                                             title={formatDateTime(task.created_at) !== '-' ? formatDateTime(task.created_at) : undefined}