chore: remove tokenlens and token usage tracking (#1357)

lib/ai/prompts.ts

@@ -117,8 +117,10 @@ export const updateDocumentPrompt = (
 ${currentContent}`;
 };
 
-export const titlePrompt = `\n
-    - you will generate a short title based on the first message a user begins a conversation with
-    - ensure it is not more than 80 characters long
-    - the title should be a summary of the user's message
-    - do not use quotes or colons`;
+export const titlePrompt = `Generate a very short chat title (2-5 words max) based on the user's message.
+Rules:
+- Maximum 30 characters
+- No quotes, colons, hashtags, or markdown
+- Just the topic/intent, not a full sentence
+- If the message is a greeting like "hi" or "hello", respond with just "New conversation"
+- Be concise: "Weather in NYC" not "User asking about the weather in New York City"`;