fix: system prompt

Author: DavidePaglieri

balrog/prompt_builder/history.py

@@ -82,6 +82,8 @@ def get_prompt(self) -> List[Message]:
             List[Message]: Messages constructed from the event history.
         """
         messages = []
+        if self.system_prompt:
+            messages.append(Message(role="user", content=self.system_prompt))
 
         # Determine which images to include
         images_needed = self.max_image_history