feat: async email slanje s cache PDF fallbackom i admin logom

Prebaci slanje emaila putnog naloga u pozadinski task bez blokiranja UI-a i dodaj fallback kad queue nije dostupna. Kod greške slanja spremi generirane PDF-ove u cache i pošalji notifikaciju s download linkovima.

Dodaj EmailDispatchLog model i Django admin pregled za praćenje kome je poslano, što je poslano, status i detalje privitaka.

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

backend/modules/fleet/migrations/0033_emaildispatchlog.py

@@ -0,0 +1,43 @@
+# Generated by Django 5.2.15 on 2026-07-21 11:50
+
+import uuid
+from django.conf import settings
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fleet', '0032_servicecontextnote'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='EmailDispatchLog',
+            fields=[
+                ('id', models.UUIDField(default=uuid.uuid4, editable=False, help_text='Unikatni identifikator entiteta (UUID).', primary_key=True, serialize=False)),
+                ('created_at', models.DateTimeField(auto_now_add=True, verbose_name='Vrijeme kreiranja')),
+                ('updated_at', models.DateTimeField(auto_now=True, verbose_name='Vrijeme zadnje izmjene')),
+                ('is_active', models.BooleanField(default=True, verbose_name='Aktivan zapis')),
+                ('dispatch_type', models.CharField(choices=[('work_order', 'Putni nalog'), ('service_record', 'Servisni zapis')], db_index=True, max_length=32, verbose_name='Tip slanja')),
+                ('recipients', models.JSONField(blank=True, default=list, verbose_name='Primatelji')),
+                ('subject', models.CharField(blank=True, max_length=255, verbose_name='Naslov')),
+                ('message', models.TextField(blank=True, verbose_name='Poruka')),
+                ('attachments', models.JSONField(blank=True, default=list, verbose_name='Privitci')),
+                ('status', models.CharField(choices=[('queued', 'U obradi'), ('sent', 'Poslano'), ('failed', 'Neuspješno')], db_index=True, default='queued', max_length=16, verbose_name='Status')),
+                ('error_message', models.TextField(blank=True, verbose_name='Greška')),
+                ('metadata', models.JSONField(blank=True, default=dict, verbose_name='Metapodaci')),
+                ('sent_at', models.DateTimeField(blank=True, null=True, verbose_name='Poslano u')),
+                ('requested_by', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='requested_email_dispatch_logs', to=settings.AUTH_USER_MODEL, verbose_name='Zatražio')),
+                ('service_record', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='email_dispatch_logs', to='fleet.vehicleservicerecord', verbose_name='Servisni zapis')),
+                ('work_order', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='email_dispatch_logs', to='fleet.workorder', verbose_name='Putni nalog')),
+            ],
+            options={
+                'verbose_name': 'Log slanja emaila',
+                'verbose_name_plural': 'Logovi slanja emaila',
+                'ordering': ['-created_at'],
+            },
+        ),
+    ]