Project: mobx
Task (challenging): Implement blog comment feature:
1) Display commenter's username with class '.comment-author' and text with '.comment-text'.
2) Add a CommentForm with a '.comment-input' textarea and a '.comment-submit-btn' below each blog.
3) Use MobX to manage comments.
4) Add undo functionality via Ctrl+Z (Windows/Linux) or Command+Z (Mac) to remove the last comment.
Constraint: DO NOT use any third-party packages; ONLY React/MobX APIs are permitted.