feat: Add created_by and cost fields to generation models, populate created_by from the authenticated user, and implement cost calculation.

models/Generation.py

@@ -2,7 +2,7 @@ from datetime import datetime, UTC
 from enum import Enum
 from typing import List, Optional
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, computed_field
 
 from models.Asset import Asset
 from models.enums import AspectRatios, Quality, GenType
@@ -34,5 +34,15 @@ class Generation(BaseModel):
     input_token_usage: Optional[int] = None
     output_token_usage: Optional[int] = None
     is_deleted: bool = False
+    album_id: Optional[str] = None
+    created_by: Optional[str] = None
     created_at: datetime = Field(default_factory=lambda: datetime.now(UTC))
     updated_at: datetime = Field(default_factory=lambda: datetime.now(UTC))
+
+    @computed_field
+    def cost(self) -> float:
+        if self.status == GenerationStatus.DONE:
+            cost_input = self.input_token_usage * 0.000002
+            cost_output = self.output_token_usage * 0.00012
+            return round(cost_input + cost_output, 3)
+        return 0.0