feat: integritet zatvaranja taska i putnog naloga

Dodaje status 'spreman_za_zavrsetak' i backend provjeru koja blokira zatvaranje taska kada je povezani putni nalog otvoren, uz 409 odgovor i opcionalni auto-close flow.\n\nPri zatvaranju putnog naloga taskovi u statusu 'servis' automatski prelaze u 'spreman_za_zavrsetak'. Frontend modal sada podržava potvrdu i retry s auto_close_work_order=true.\n\nUključeni su i ciljani testovi za novi behavior, te ažuriran prikaz statusa u dashboardu.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/modules/fleet/tests/test_services.py

@@ -3,6 +3,7 @@ from django.test import TestCase
 from django.contrib.auth import get_user_model
 from modules.fleet.services import VehicleService
 from modules.fleet.models import Vehicle, WorkOrder, VehicleServiceRecord
+from modules.task_management.models import Task
 
 
 class FleetServiceTests(TestCase):
@@ -49,4 +50,26 @@ class FleetServiceTests(TestCase):
         
         # Nalog sa završnom kilometražom
         wo.end_mileage = 1100
-        assert wo.distance == 100
+        assert wo.distance == 100
+
+    def test_closing_work_order_moves_task_to_ready_for_completion(self):
+        work_order = WorkOrder.objects.create(
+            vehicle=self.vehicle,
+            creator=self.user,
+            purpose="kontrola",
+            status="open",
+            start_mileage=5000,
+            end_mileage=5200,
+        )
+        task = Task.objects.create(
+            title="Servis",
+            description="",
+            status="servis",
+            assigned_to=self.user,
+            vehicle=self.vehicle,
+            work_order=work_order,
+        )
+
+        VehicleService.update_work_order(work_order, {"status": "closed"})
+        task.refresh_from_db()
+        self.assertEqual(task.status, "spreman_za_zavrsetak")