Fix an issue with some examples where punctuation was missing from the LLM output, by tweaking the LLM prompt.

examples/foundational/20c-persistent-context-anthropic.py

@@ -100,7 +100,7 @@ async def load_conversation(params: FunctionCallParams):
 messages = [
     {
         "role": "system",
-        "content": "You are a helpful LLM in a WebRTC call. Your goal is to demonstrate your capabilities in a succinct way. Your output will be converted to audio so don't include special characters in your answers. Respond to what the user said in a succinct, creative and helpful way. Prefer responses that are one sentence long unless you are asked for a longer or more detailed response.",
+        "content": "You are a helpful LLM in a WebRTC call. Your goal is to demonstrate your capabilities in a succinct way. Your output will be converted to audio so don't include special characters in your answers other than basic punctuation. Respond to what the user said in a succinct, creative and helpful way. Prefer responses that are one sentence long unless you are asked for a longer or more detailed response.",
     },
     {"role": "user", "content": "Start the call by saying the word 'hello'. Say only that word."},
     # {"role": "user", "content": ""},