Refactor catalog tables for responsive layout

[saahithjanapati]

Summary

• replace the catalog table markup with accessible, responsive course cards while preserving expand/collapse behavior
• add a structured header that surfaces semester selection, last-updated metadata, and bulk expand controls
• rebuild the catalog styles to support mobile-friendly stacking, desktop grid layouts, and theme-aware colors

Testing

• CI=true npm test (fails: react-scripts missing because dependencies could not be installed in this environment)
• npm install (fails: npm registry returned 403 for tsutils so dependencies are unavailable)

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

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