feat: async PDF cache i API media putanje za putne naloge

Uvodi background request tok za generiranje PDF-a s 24h cache-om i cleanup taskom preko Celery beat-a. Dodaje notification metadata download_url za ponovno preuzimanje bez regeneracije, API image endpointe za putne naloge i račune, te frontend integraciju za async download i produkcijski prikaz slika.

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

backend/modules/fleet/models.py

@@ -54,6 +54,15 @@ def _work_order_photo_upload_to(instance, filename):
     unique_name = f"{uuid.uuid4().hex}_{filename}"
     return f"fleet/{vehicle_reg}/work_order_photos/{unique_name}"
 
+def _generated_work_order_pdf_upload_to(instance, filename):
+    vehicle_reg = 'unknown'
+    try:
+        vehicle_reg = instance.work_order.vehicle.registration_number
+    except Exception:
+        vehicle_reg = 'unknown'
+    unique_name = f"{uuid.uuid4().hex}_{filename}"
+    return f"fleet/{vehicle_reg}/generated_pdfs/{unique_name}"
+
 
 class VehicleServicePhoto(BaseModel):
     """
@@ -384,6 +393,48 @@ class WorkOrderPhoto(BaseModel):
         return f"WorkOrderPhoto {self.pk} ({self.work_order_id})"
 
 
+class GeneratedWorkOrderPdf(BaseModel):
+    PDF_TYPE_CHOICES = [
+        ('work_order', _("Putni nalog")),
+        ('service_records', _("Servisni zapisi")),
+        ('invoices', _("Računi")),
+    ]
+    STATUS_CHOICES = [
+        ('pending', _("U obradi")),
+        ('ready', _("Spremno")),
+        ('failed', _("Neuspješno")),
+    ]
+
+    work_order = models.ForeignKey(
+        WorkOrder,
+        on_delete=models.CASCADE,
+        related_name='generated_pdfs',
+        verbose_name=_("Putni nalog"),
+    )
+    requested_by = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        null=True,
+        blank=True,
+        on_delete=models.SET_NULL,
+        related_name='requested_generated_work_order_pdfs',
+        verbose_name=_("Zatražio"),
+    )
+    pdf_type = models.CharField(max_length=32, choices=PDF_TYPE_CHOICES, db_index=True, verbose_name=_("Tip PDF-a"))
+    status = models.CharField(max_length=16, choices=STATUS_CHOICES, default='pending', db_index=True, verbose_name=_("Status"))
+    file = models.FileField(upload_to=_generated_work_order_pdf_upload_to, null=True, blank=True, verbose_name=_("PDF datoteka"))
+    filename = models.CharField(max_length=255, blank=True, verbose_name=_("Naziv datoteke"))
+    expires_at = models.DateTimeField(null=True, blank=True, db_index=True, verbose_name=_("Vrijedi do"))
+    error_message = models.TextField(blank=True, verbose_name=_("Poruka greške"))
+
+    class Meta:
+        verbose_name = _("Generirani PDF putnog naloga")
+        verbose_name_plural = _("Generirani PDF-ovi putnih naloga")
+        ordering = ['-created_at']
+
+    def __str__(self):
+        return f"{self.pdf_type}:{self.work_order_id}:{self.status}"
+
+
 class VehicleServiceRecord(BaseModel):
     """
     Zapisi o servisima/popravcima na vozilu.