feat: async PDF cache i API media putanje za putne naloge

Uvodi background request tok za generiranje PDF-a s 24h cache-om i cleanup taskom preko Celery beat-a. Dodaje notification metadata download_url za ponovno preuzimanje bez regeneracije, API image endpointe za putne naloge i račune, te frontend integraciju za async download i produkcijski prikaz slika.

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

backend/modules/fleet/tests/test_work_order_images_endpoint.py

@@ -7,7 +7,7 @@ import uuid
 from io import BytesIO
 from PIL import Image
 
-from modules.fleet.models import Vehicle, WorkOrder, VehicleServiceRecord, VehicleServicePhoto
+from modules.fleet.models import Vehicle, WorkOrder, WorkOrderInvoice, VehicleServiceRecord, VehicleServicePhoto
 
 
 def create_test_image(filename='test.jpg', size=(40, 40), color='red'):
@@ -94,3 +94,47 @@ class WorkOrderImagesEndpointTests(TestCase):
         response = self.client.get(service_photos_url)
         self.assertEqual(response.status_code, 200)
         self.assertEqual(len(response.data), 0)
+
+    def test_work_order_images_endpoint_returns_api_file_urls(self):
+        upload_url = reverse('workorder-images', kwargs={'pk': self.work_order.pk})
+        create_response = self.client.post(
+            upload_url,
+            data={
+                'image': create_test_image('workorder-url.jpg'),
+                'description': 'URL test',
+            },
+            format='multipart',
+        )
+        self.assertEqual(create_response.status_code, 201, create_response.data)
+
+        list_response = self.client.get(upload_url)
+        self.assertEqual(list_response.status_code, 200)
+        images = list_response.data.get('images', [])
+        self.assertEqual(len(images), 1)
+
+        photo_id = images[0]['id']
+        self.assertIn('/api/fleet/work-orders/', images[0]['original_url'])
+        self.assertIn(f'/images/{photo_id}/file', images[0]['original_url'])
+
+        file_response = self.client.get(images[0]['original_url'])
+        self.assertEqual(file_response.status_code, 200)
+        self.assertTrue(file_response['Content-Type'].startswith('image/'))
+
+    def test_work_order_invoice_serializer_exposes_image_api_url(self):
+        invoice = WorkOrderInvoice.objects.create(
+            work_order=self.work_order,
+            naziv_racuna='Test račun',
+            image=create_test_image('invoice.jpg'),
+            created_by=self.user,
+        )
+        list_url = f"{reverse('work-order-invoice-list')}?work_order_id={self.work_order.pk}"
+        list_response = self.client.get(list_url)
+        self.assertEqual(list_response.status_code, 200)
+        self.assertEqual(len(list_response.data), 1)
+        image_url = list_response.data[0].get('image_url')
+        self.assertIsNotNone(image_url)
+        self.assertIn(f'/api/fleet/work-order-invoices/{invoice.pk}/image/', image_url)
+
+        image_response = self.client.get(image_url)
+        self.assertEqual(image_response.status_code, 200)
+        self.assertTrue(image_response['Content-Type'].startswith('image/'))