Add advisor mention with link on About page intro

[He-jiazhi]

Motivation

• Include advisor information on the main About paragraph so the homepage clearly shows Ph.D. supervision and links to the advisor's profile.

Description

• Updated _pages/about.md to add "advised by Prof. Yu Cheng" in the first intro paragraph.

Testing

• Verified the markdown change with git diff _pages/about.md and committed the update successfully; this check passed.
• Attempted bundle exec jekyll build but it failed due to missing Jekyll/bundler and bundle install failing with Rubygems 403 Forbidden.
• Attempted a Playwright screenshot of a local server at 127.0.0.1:4000 but it failed because the site server was not running, producing ERR_EMPTY_RESPONSE.

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Codex Task