feat: add catalogue image management (#1)

- Add CatalogueImage model with FK to Product
- Add image resize service (strict/non-strict modes with configurable dimensions)
- Add CRUD API endpoints with admin-only write permissions
- Add catalogue_images field to product listing/detail endpoints
- Serve media files in development via static()
- 28 TDD tests covering model, API, permissions, resize, and product listing

tienda_ilusion/don_confiao/models/catalogue_images.py

@@ -0,0 +1,20 @@
+from django.db import models
+
+from .products import Product
+
+
+def _catalogue_image_upload_path(instance, filename):
+    return f"catalogue_images/{instance.product_id}/{filename}"
+
+
+class CatalogueImage(models.Model):
+    product = models.ForeignKey(
+        Product,
+        on_delete=models.CASCADE,
+        related_name="catalogue_images",
+    )
+    image = models.ImageField(upload_to=_catalogue_image_upload_path)
+    uploaded_at = models.DateTimeField(auto_now_add=True)
+
+    def __str__(self):
+        return f"CatalogueImage for {self.product.name} ({self.id})"