Add multi-image compositions, docker setup, tests, and docs

- Add CompositionImage model with multi-image upload and main image flag
- Add composition endpoints: add-images, set-main-image, delete image, by-created-at filter
- Make contact-us by_category public
- Add 24 API tests covering all endpoints
- Add Dockerfile, docker-compose, entrypoint and docker docs
- Add Persian API docs and update README and Postman collection

Co-authored-by: Cursor <cursoragent@cursor.com>

api/models.py

@@ -49,6 +49,8 @@ class Composition(models.Model):
     """
     name = models.CharField(max_length=200, verbose_name='نام')
     description = models.TextField(verbose_name='توضیحات')
+    # Legacy single-image field, kept for backward compatibility.
+    # New uploads use the related CompositionImage model below.
     image = models.ImageField(
         upload_to='compositions/',
         verbose_name='تصویر',
@@ -68,6 +70,56 @@ class Composition(models.Model):
     
     def __str__(self):
         return self.name
+    
+    @property
+    def main_image(self):
+        """Return the image flagged as main, falling back to the first image."""
+        return self.images.filter(is_main=True).first() or self.images.first()
+
+
+class CompositionImage(models.Model):
+    """
+    Image belonging to a Composition. A composition can have many images,
+    and at most one of them can be flagged as the main image.
+    """
+    composition = models.ForeignKey(
+        Composition,
+        on_delete=models.CASCADE,
+        related_name='images',
+        verbose_name='ترکیب'
+    )
+    image = models.ImageField(
+        upload_to='compositions/',
+        verbose_name='تصویر'
+    )
+    is_main = models.BooleanField(default=False, verbose_name='تصویر اصلی')
+    created_at = models.DateTimeField(auto_now_add=True, verbose_name='تاریخ ایجاد')
+    
+    class Meta:
+        verbose_name = 'تصویر ترکیب'
+        verbose_name_plural = 'تصاویر ترکیب'
+        # Main image first, then newest.
+        ordering = ['-is_main', '-created_at']
+        constraints = [
+            # At most one main image per composition.
+            models.UniqueConstraint(
+                fields=['composition'],
+                condition=models.Q(is_main=True),
+                name='unique_main_image_per_composition'
+            )
+        ]
+    
+    def __str__(self):
+        return f"{self.composition.name} - {'main' if self.is_main else 'image'} #{self.pk}"
+    
+    def save(self, *args, **kwargs):
+        # Ensure only one main image per composition: if this one is being
+        # set as main, unset the flag on the others.
+        if self.is_main:
+            CompositionImage.objects.filter(
+                composition=self.composition, is_main=True
+            ).exclude(pk=self.pk).update(is_main=False)
+        super().save(*args, **kwargs)
 
 
 class Campaign(models.Model):