feat: Implement external generation import API secured by HMAC-SHA256 signature verification.

api/models/ExternalGenerationDTO.py

@@ -0,0 +1,37 @@
+from typing import Optional
+from pydantic import BaseModel, Field
+from models.enums import AspectRatios, Quality
+
+
+class ExternalGenerationRequest(BaseModel):
+    """Request model for importing external generations."""
+    
+    prompt: str
+    tech_prompt: Optional[str] = None
+    
+    # Image can be provided as base64 string OR URL (one must be provided)
+    image_data: Optional[str] = Field(None, description="Base64-encoded image data")
+    image_url: Optional[str] = Field(None, description="URL to download image from")
+    
+    # Generation metadata
+    aspect_ratio: AspectRatios = AspectRatios.NINESIXTEEN
+    quality: Quality = Quality.ONEK
+    
+    # Optional linking
+    linked_character_id: Optional[str] = None
+    created_by: str = Field(..., description="User ID from external system")
+    project_id: Optional[str] = None
+    
+    # Performance metrics
+    execution_time_seconds: Optional[float] = None
+    api_execution_time_seconds: Optional[float] = None
+    token_usage: Optional[int] = None
+    input_token_usage: Optional[int] = None
+    output_token_usage: Optional[int] = None
+    
+    def validate_image_source(self):
+        """Ensure at least one image source is provided."""
+        if not self.image_data and not self.image_url:
+            raise ValueError("Either image_data or image_url must be provided")
+        if self.image_data and self.image_url:
+            raise ValueError("Only one of image_data or image_url should be provided")