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/task_management/services.py

@@ -6,6 +6,7 @@ from django.core.exceptions import ValidationError as DjangoValidationError
 import logging
 
 from .models import Task, TaskTemplate, TaskWorkEntry
+from .exceptions import OpenWorkOrderBlockingTaskClose
 from modules.fleet.models import VehicleServiceRecord
 
 logger = logging.getLogger(__name__)
@@ -106,10 +107,34 @@ class TaskService:
             )
 
     @staticmethod
-    def update_task_entry(instance, data, user):
+    def update_task_entry(instance, data, user, auto_close_work_order=False):
         if not user.is_staff and instance.assigned_to != user:
             raise ValidationError("Nemate dozvolu za izmjenu ovog zadatka.")
 
+        target_status = data.get('status', instance.status)
+        target_work_order = data.get('work_order', instance.work_order)
+        closing_statuses = {'neaktivan', 'zavrsen'}
+
+        if target_status in closing_statuses:
+            if not target_work_order:
+                raise ValidationError({"work_order": "Putni nalog je obavezan prije zatvaranja zadatka."})
+            if target_work_order.status == 'open':
+                if not auto_close_work_order:
+                    work_order_label = f"WO-{str(target_work_order.id).split('-')[0].upper()}"
+                    raise OpenWorkOrderBlockingTaskClose(detail={
+                        "code": "OPEN_WORK_ORDER_BLOCKING_TASK_CLOSE",
+                        "message": f"Putni nalog {work_order_label} je još otvoren. Želite li ga automatski zatvoriti?",
+                        "work_order_id": str(target_work_order.id),
+                        "work_order_label": work_order_label,
+                    })
+                if target_work_order.end_mileage is None:
+                    raise ValidationError({
+                        "work_order": "Automatsko zatvaranje putnog naloga nije moguće bez završne kilometraže."
+                    })
+                from modules.fleet.services import VehicleService
+                target_work_order = VehicleService.update_work_order(target_work_order, {"status": "closed"})
+                data['work_order'] = target_work_order
+
         for attr, value in data.items():
             if attr == 'template_id':
                 continue