feat: dodaj display_code polje za putne naloge (MT070626 format)

- Dodano polje 'display_code' na WorkOrder model (format: 2 inicijala + ddmmyy)
- Migracije za kreiranje polja i backfill postojećih naloga
- Ažuriran WorkOrderSerializer za validaciju i serijalizaciju display_code
- Backend tasks za auto-generiranje display_code pri kreiranju
- Frontend komponente ažurirane za prikaz display_code umjesto UUID:
  * FleetDashboardShell tablica putnih naloga
  * WorkOrderDetailModal
  * TaskCreateModal
  * Sve PDF stranice
- displayIds.js utility za formatiranjeDisplay ID-eva
- Admin interface prikazuje display_code

backend/modules/fleet/migrations/0025_workorder_display_code.py

@@ -0,0 +1,24 @@
+# Generated by Django 5.2.15 on 2026-07-17 21:55
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fleet', '0024_alter_workorderphoto_created_at_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='workorder',
+            name='display_code',
+            field=models.CharField(
+                blank=True,
+                db_index=True,
+                help_text='Format: MT070626 (2 slova + 6 znamenki).',
+                max_length=8,
+                verbose_name='Prikaz putnog naloga',
+            ),
+        ),
+    ]

backend/modules/fleet/migrations/0026_backfill_workorder_display_code.py

@@ -0,0 +1,30 @@
+from django.db import migrations
+
+
+def backfill_workorder_display_code(apps, schema_editor):
+    WorkOrder = apps.get_model('fleet', 'WorkOrder')
+    for work_order in WorkOrder.objects.select_related('creator').all():
+        current_code = str(getattr(work_order, 'display_code', '') or '').strip().upper()
+        if current_code:
+            continue
+        creator = getattr(work_order, 'creator', None)
+        first_name = str(getattr(creator, 'first_name', '') or '').strip()
+        last_name = str(getattr(creator, 'last_name', '') or '').strip()
+        if not first_name or not last_name:
+            continue
+        order_date = getattr(work_order, 'date', None)
+        if not order_date:
+            continue
+        display_code = f"{first_name[0].upper()}{last_name[0].upper()}{order_date.strftime('%d%m%y')}"
+        WorkOrder.objects.filter(pk=work_order.pk).update(display_code=display_code)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fleet', '0025_workorder_display_code'),
+    ]
+
+    operations = [
+        migrations.RunPython(backfill_workorder_display_code, migrations.RunPython.noop),
+    ]