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/admin.py

@@ -44,7 +44,7 @@ class ServiceAttachmentInline(admin.TabularInline):
 class WorkOrderInline(admin.TabularInline):
     model = WorkOrder
     extra = 0
-    fields = ('display_code', 'creator', 'date', 'start_mileage', 'end_mileage', 'location', 'travel_start_at', 'travel_end_at', 'purpose', 'status')
+    fields = ('display_code', 'creator', 'date', 'start_mileage', 'end_mileage', 'origin_location', 'location', 'travel_start_at', 'travel_end_at', 'purpose', 'status')
     readonly_fields = ('date',)
 
 
@@ -176,7 +176,7 @@ class CraneAdmin(VehicleAdmin):
 
 @admin.register(WorkOrder)
 class WorkOrderAdmin(admin.ModelAdmin):
-    list_display = ('display_code', 'id', 'vehicle', 'creator', 'date', 'location', 'travel_start_at', 'travel_end_at', 'start_mileage', 'end_mileage', 'distance_display', 'status')
+    list_display = ('display_code', 'id', 'vehicle', 'creator', 'date', 'origin_location', 'location', 'travel_start_at', 'travel_end_at', 'start_mileage', 'end_mileage', 'distance_display', 'status')
     list_filter = ('status', 'date', 'vehicle')
     search_fields = ('display_code', 'vehicle__registration_number', 'creator__username', 'purpose')
     readonly_fields = ('date',)