fix: Clarify topic extraction instructions in the TopicService to specify that the output should be a single sentence capturing the main idea.

services/topic_service.py

@@ -79,7 +79,7 @@ class TopicService:
             raise ValueError("Text cannot be empty")
         
         system_message = """You are an information extraction model.
-Extract a detailed topic from the user text.
+Extract a topic from the user text. The topic should be a single sentence that captures the main idea of the text.
 
 Examples:
 - Text: "Governments should subsidize electric cars to encourage adoption."