Refactor catalog layout for responsive cards

[saahithjanapati]

Summary

• replace the catalog table rendering with responsive course cards that better support all screen sizes
• update catalog styling to introduce grid-based session rows, mobile stacking, and refreshed button treatments
• retain expand/collapse behaviors and metadata controls while improving accessibility semantics

Testing

• npm install (fails: 403 Forbidden fetching tsutils from registry)

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https://chatgpt.com/codex/tasks/task_e_68d5631447cc83289b1bf27dadf50a2e

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