Add auto-follow camera setting with toggleable UI control

[saahithjanapati]

Summary

• add a shared settings context that defaults to the new auto-follow camera mode and persists it in localStorage
• surface a settings modal with a toggle so users can disable automatic centering when they prefer manual control
• update the catalog page to center the viewport on the active course when auto-follow is enabled and tune styles for the new UI

Testing

• npm test -- --watch=false (fails: legacy App.test.js still expects the CRA boilerplate "learn react" link)

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https://chatgpt.com/codex/tasks/task_e_68eb4415d5dc832892b088b26e257e1f

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