feat: dodaj ishodište i PDF račune za putni nalog

Dodano je origin_location polje kroz backend model, serializer, admin i UI
modal za kreiranje/uređivanje putnog naloga (default: Zagreb).

Računi putnog naloga sada prihvaćaju slike i PDF datoteke, uz backend
validaciju formata, podršku za serving PDF-a i prilagodbu preview prikaza.

Za greške uploada računa dodan je error toast kako bi poruke validacije bile
vidljive korisniku odmah u sučelju.

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

backend/modules/fleet/views.py

@@ -3,6 +3,7 @@
 from io import BytesIO
 import base64
 from datetime import timedelta
+from pathlib import Path
 
 from PIL import Image, UnidentifiedImageError
 from django.conf import settings
@@ -401,6 +402,7 @@ def _build_work_order_pdf(work_order):
     transport_total = float(work_order.servicer_vehicle_fuel_cost or 0.0)
     grand_total = daily_total + transport_total
     place_label = (work_order.location or 'Zagreb').split(',')[0].strip() or 'Zagreb'
+    origin_label = (work_order.origin_location or 'Zagreb').split(',')[0].strip() or 'Zagreb'
     invoice_names = [inv.naziv_racuna for inv in invoices[:5] if inv.naziv_racuna]
     attachments_text = ', '.join(invoice_names) if invoice_names else '-'
     assigned_servicer_vehicle = (
@@ -598,7 +600,7 @@ def _build_work_order_pdf(work_order):
         y,
         [
             ["RELACIJA od", "RELACIJA do", "Vrsta prijevoznog sredstva", "Razred [km]", "Iznos za prijevoz", "Ukupan iznos"],
-            [place_label or '-', work_order.location or '-', f"{servicer_vehicle_label}, {servicer_vehicle_registration}", str(work_order.distance or 0), _fmt_eur(transport_total), _fmt_eur(transport_total)],
+            [origin_label or '-', work_order.location or '-', f"{servicer_vehicle_label}, {servicer_vehicle_registration}", str(work_order.distance or 0), _fmt_eur(transport_total), _fmt_eur(transport_total)],
             ["", "", "", "", "", ""],
             ["", "", "", "", "", ""],
         ],
@@ -1601,7 +1603,7 @@ class WorkOrderViewSet(viewsets.ModelViewSet):
                     <td>{escape(invoice.lokacija or '-')}</td>
                     <td>{escape(datum)}</td>
                     <td>{escape(invoice.opis or '-')}</td>
-                    <td>{f'<a href="{escape(image_url)}" target="_blank" rel="noopener noreferrer">Otvori sliku</a>' if image_url else '-'}</td>
+                    <td>{f'<a href="{escape(image_url)}" target="_blank" rel="noopener noreferrer">Otvori dokument</a>' if image_url else '-'}</td>
                 </tr>
                 """
             )
@@ -1791,6 +1793,17 @@ class WorkOrderInvoiceViewSet(viewsets.ModelViewSet):
         if not invoice.image:
             raise DRFValidationError({"detail": "Slika računa nije dostupna."})
 
+        suffix = Path(invoice.image.name or '').suffix.lower()
+        if suffix == '.pdf':
+            invoice.image.open('rb')
+            try:
+                response = HttpResponse(invoice.image.read(), content_type='application/pdf')
+            finally:
+                invoice.image.close()
+            response['Cache-Control'] = 'private, max-age=86400'
+            response['Content-Disposition'] = f'inline; filename="invoice-{invoice.pk}.pdf"'
+            return response
+
         width = _parse_positive_int(
             request.query_params.get('w'),
             field_name='w',