F(backend): add public media derivatives pipeline

apps/gallery/api/schemas.py

@@ -5,6 +5,7 @@ from typing import Optional
 
 from apps.blog.api.schemas import AuthorSchema
 from apps.gallery.models import Gallery
+from core.media import BLUR_VARIANT, PREVIEW_VARIANT, derivative_url
 
 
 class GallerySchema(ModelSchema):
@@ -12,12 +13,34 @@ class GallerySchema(ModelSchema):
     uploaded_by: AuthorSchema
     file_size_mb: float
     markdown_url: str
+    absolute_image_url: Optional[str] = None
+    absolute_image_preview_url: Optional[str] = None
+    absolute_image_blur_url: Optional[str] = None
 
     class Config:
         model = Gallery
         model_fields = ['id', 'title', 'description', 'image', 'alt_text',
                         'width', 'height', 'is_public', 'created_at']
 
+    @staticmethod
+    def resolve_absolute_image_url(obj, context):
+        request = context["request"]
+        if obj.image and hasattr(obj.image, "url"):
+            return request.build_absolute_uri(obj.image.url)
+        return None
+
+    @staticmethod
+    def resolve_absolute_image_preview_url(obj, context):
+        request = context["request"]
+        url = derivative_url(obj.image, PREVIEW_VARIANT)
+        return request.build_absolute_uri(url) if url else None
+
+    @staticmethod
+    def resolve_absolute_image_blur_url(obj, context):
+        request = context["request"]
+        url = derivative_url(obj.image, BLUR_VARIANT)
+        return request.build_absolute_uri(url) if url else None
+
 
 class GalleryCreateSchema(Schema):
     """Payload for creating a gallery entry."""