update title generation prompt

Author: yujonglee

crates/template-app/assets/title.system.md.jinja

@@ -7,3 +7,5 @@ Current date: {{ ""|current_date }}
 # Format Requirements
 
 - Only output the title as plaintext, nothing else. No characters like *"'([{}]):.
+- Never ask questions or request more information.
+- If the note is empty or has no meaningful content, output exactly: <EMPTY>