feat: handle 429 errors and redirect to rate-limited page

[0xi4o]

• Adds a rate-limited page
• Handle 429 TOO MANY REQUESTS errors and redirect to rate-limited page

[gemini-code-assist[bot]]

Summary of Changes

Hello @0xi4o, I'm Gemini Code Assist[^1]! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the application's robustness and user experience by gracefully handling API rate-limiting scenarios. It introduces a new user interface to inform users about rate limits and provides a mechanism to automatically redirect them to this page when a 429 error occurs, along with a countdown before they can retry their actions.

Highlights

• New Rate-Limited Page: Introduced a dedicated RateLimitedPage component to inform users when they have exceeded API rate limits, providing a clear message and a countdown timer.
• 429 Error Handling: Implemented global error handling within ErrorContext to detect HTTP 429 (Too Many Requests) errors and automatically redirect users to the new rate-limited page. The retry-after header is used to set the initial countdown.
• User Experience: The new page includes a 'Try Again' button that becomes active after the countdown, and a 'Back to Home' button for authenticated users, improving the user experience during rate-limiting events.

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[0xi4o]

What will happen when LLM provider returns a 429 error? Will user be redirected to this 429 page or The error message (e.g., “429: Rate limit exceeded”) will appear directly in the chat box?

When LLM providers return a 429 error, we catch it and return a 500 to the frontend. So those won't redirect to the rate-limited page.