Add Yang Li's profile as PhD student

[Yang-Li86]

Summary

Adds Yang Li's team profile under content/authors/Yang/, following the README's "How To Add Your Profile" instructions:

• _index.md — PhD Student role, KCL affiliation, research interests (Federated Learning, Distributed Optimization, Surgical Data Science, IoT), links to email / LinkedIn / Google Scholar / GitHub, user_groups: [PhD Students], and a short bio
• avatar.jpg — square headshot in the page bundle

Testing

• Full hugo build passes
• Verified with hugo server: profile page renders at /author/yang-li/ with avatar and links, and the entry appears in the homepage Team section and on the People page

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