feat: vise taskova po putnom nalogu i izmjena podataka dizalice

- task_management/views.py: dodaj ?work_order= filter u get_queryset
  (jedini razlog zasto putni nalog nije mogao imati vise taskova bio je
  nedostatak backend filtera; model uvijek podrzavao vise taskova)
- fleet/serializers.py: ukloni current_mileage iz read_only_fields
  kako bi se moglo azurirati putem PATCH /fleet/cranes/{id}/
- fleetDashboardStore.js: dodaj fetchTasksByWorkOrder(workOrderId)
  koji dohvaca GET tasks/tasks/?work_order={id}
- WorkOrderDetailModal.jsx:
  * import TaskCreateModal, fetchTasksByWorkOrder, updateVehicle, getStatusLabel
  * nova sekcija 'Zadaci putnog naloga' s popisom i gumbom '+ Dodaj zadatak'
  * gumb '🔧 Izmijeni podatke dizalice' otvara CraneDataModal
  * CraneDataModal: unos superstructure_working_hours, chassis_working_hours,
    current_mileage; poziva updateVehicle; prikazuje trenutne vrijednosti
    kao placeholder

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

frontend/src/stores/fleetDashboardStore.js

@@ -721,6 +721,14 @@ export async function fetchWorkOrderById(workOrderId) {
     return await api.get(`fleet/work-orders/${encodeURIComponent(workOrderId)}/`);
 }
 
+export async function fetchTasksByWorkOrder(workOrderId) {
+    if (!workOrderId) {
+        return [];
+    }
+    const data = await api.get(`tasks/tasks/?work_order=${encodeURIComponent(workOrderId)}`);
+    return Array.isArray(data) ? data : (data?.results ?? []);
+}
+
 export async function fetchWorkOrderTaskServiceContext(workOrderId) {
     if (!workOrderId) {
         return { tasks: [], additional_costs_table: null };