fix: append nag reminder instead of inserting at front (#142)

The reminder was inserted at index 0, placing a text block before
tool_result blocks in the user message content array. Use append
to keep the reminder at the end, consistent with message ordering.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: alsaberi

agents/s03_todo_write.py

@@ -187,7 +187,7 @@ def agent_loop(messages: list):
                     used_todo = True
         rounds_since_todo = 0 if used_todo else rounds_since_todo + 1
         if rounds_since_todo >= 3:
-            results.insert(0, {"type": "text", "text": "<reminder>Update your todos.</reminder>"})
+            results.append({"type": "text", "text": "<reminder>Update your todos.</reminder>"})
         messages.append({"role": "user", "content": results})