feat: Introduce generation grouping, enabling multiple generations per request via a new count parameter and retrieval by group ID.

models/Generation.py

@@ -35,6 +35,7 @@ class Generation(BaseModel):
     output_token_usage: Optional[int] = None
     is_deleted: bool = False
     album_id: Optional[str] = None  
+    generation_group_id: Optional[str] = None
     created_by: Optional[str] = None  # Stores User ID (Telegram ID or Web User ObjectId)
     project_id: Optional[str] = None
     created_at: datetime = Field(default_factory=lambda: datetime.now(UTC))