fix: prikazi napomenu iz DB u servisnom PDF-u

Servisni PDF sada koristi work_order.notes za polje Napomene umjesto izvedenog teksta iz task naslova. Dodana je i invalidacija generated PDF cachea pri updateu putnog naloga kako bi se nakon spremanja napomene uvijek generirao svjezi PDF.

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

backend/modules/fleet/views.py

@@ -845,8 +845,7 @@ def _build_work_order_service_records_pdf(work_order):
         .order_by('service_date', 'created_at')
     )
     related_tasks = list(_work_order_related_tasks_queryset(work_order))
-    task_titles = [row.task.title for row in service_rows if getattr(row, 'task', None) and row.task.title]
-    notes_text = ' | '.join(task_titles[:2]) if task_titles else (work_order.notes or '')
+    notes_text = str(work_order.notes or '').strip()
 
     buffer = BytesIO()
 
@@ -1715,6 +1714,10 @@ class WorkOrderViewSet(viewsets.ModelViewSet):
     def get_queryset(self):
         return _work_orders_queryset_for_user(self.request.user)
 
+    def perform_update(self, serializer):
+        work_order = serializer.save()
+        _invalidate_work_order_pdf_cache(work_order, pdf_types=['work_order', 'service_records', 'invoices'])
+
     @action(detail=True, methods=['get', 'post'], url_path='images', parser_classes=[MultiPartParser, FormParser])
     def images(self, request, pk=None):
         work_order = self.get_object()