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/serializers.py

@@ -1,5 +1,6 @@
 from rest_framework import serializers
 import re
+from pathlib import Path
 from django.urls import reverse
 from django.utils import timezone
 from .models import (
@@ -104,7 +105,7 @@ class WorkOrderSerializer(serializers.ModelSerializer):
             'servicer_vehicle_registration', 'servicer_vehicle_make_model',
             'servicer_vehicle_start_mileage', 'servicer_vehicle_end_mileage',
             'servicer_vehicle_fuel_cost',
-            'location', 'travel_start_at', 'travel_end_at',
+            'origin_location', 'location', 'travel_start_at', 'travel_end_at',
             'purpose', 'notes', 'status'
         ]
         read_only_fields = ['id', 'date']
@@ -119,6 +120,7 @@ class WorkOrderSerializer(serializers.ModelSerializer):
             'servicer_vehicle_start_mileage': {'required': False, 'allow_null': True},
             'servicer_vehicle_end_mileage': {'required': False, 'allow_null': True},
             'servicer_vehicle_fuel_cost': {'required': False, 'allow_null': True},
+            'origin_location': {'required': False, 'allow_blank': True},
             'location': {'required': False, 'allow_blank': True},
             'travel_start_at': {'required': False, 'allow_null': True},
             'travel_end_at': {'required': False, 'allow_null': True},
@@ -211,6 +213,7 @@ class WorkOrderSerializer(serializers.ModelSerializer):
 
 class WorkOrderInvoiceSerializer(serializers.ModelSerializer):
     image_url = serializers.SerializerMethodField()
+    image_content_type = serializers.SerializerMethodField()
 
     class Meta:
         model = WorkOrderInvoice
@@ -223,6 +226,7 @@ class WorkOrderInvoiceSerializer(serializers.ModelSerializer):
             'opis',
             'image',
             'image_url',
+            'image_content_type',
             'created_by',
             'created_at',
         ]
@@ -238,6 +242,31 @@ class WorkOrderInvoiceSerializer(serializers.ModelSerializer):
             reverse('work-order-invoice-image', kwargs={'pk': obj.pk})
         )
 
+    def get_image_content_type(self, obj):
+        if not obj.image:
+            return None
+        suffix = Path(obj.image.name or '').suffix.lower()
+        if suffix == '.pdf':
+            return 'application/pdf'
+        if suffix in {'.jpg', '.jpeg'}:
+            return 'image/jpeg'
+        if suffix == '.png':
+            return 'image/png'
+        if suffix == '.webp':
+            return 'image/webp'
+        if suffix == '.gif':
+            return 'image/gif'
+        return 'application/octet-stream'
+
+    def validate_image(self, value):
+        if not value:
+            return value
+        suffix = Path(getattr(value, 'name', '')).suffix.lower()
+        allowed_suffixes = {'.jpg', '.jpeg', '.png', '.webp', '.gif', '.pdf'}
+        if suffix not in allowed_suffixes:
+            raise serializers.ValidationError('Datoteka računa mora biti slika (.jpg, .jpeg, .png, .webp, .gif) ili PDF (.pdf).')
+        return value
+
 
 class WorkOrderPhotoSerializer(serializers.ModelSerializer):
     class Meta: