feat: dodaj mjesecni izvjestaj servisera i troskova u kalendar widget

- Dva nova Django API endpointa (GET /api/fleet/reports/monthly-servicer/ i
  /api/fleet/reports/monthly-costs/) koji generiraju DOCX u A4 landscape formatu
- TaskCalendarWidget prosiren s report panelom: dva gumba iznad kalendara
  (Izvjestaj servisera / Izvjestaj troskova) sirenjem drawer-a na 680 px
- Preview tablice s podacima iz postojeceg tasks/workOrders store-a
- downloadMonthlyServiserReport i downloadMonthlyCostsReport u store-u
- TaskCalendarPortal prosljeduje activeWorkOrders prop widgetu

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

frontend/src/components/layout/TaskCalendarPortal.jsx

@@ -103,6 +103,7 @@ export default function TaskCalendarPortal() {
             <TaskCalendarWidget
                 tasks={tasks}
                 notes={notes}
+                workOrders={activeWorkOrders}
                 onTaskClick={handleTaskClick}
             />
             <ServiceNotesWidget