TraceAI workspace and landing page refresh

A dedicated /ai study workspace, a smoother TraceAI panel, and a faster, clearer landing page for new visitors.

• TraceAI has a full-page experience at /ai for STEM questions, explanations, and study help.
• In-app TraceAI gained a settings panel, better mobile layout, and improved chat UI.
• The public landing page was rebuilt for clearer sections, performance, and calls to action.
• Join the Team applications page (/apply) has clearer status labels and layout for applicants.