feat: add browser example and sandbox CORS support

[aaishmeen]

Closes #2

Summary

Adds a browser-based example under examples/browser demonstrating SmoothAPI's core resilience features:

• Retry behavior using /unstable-data
• Circuit breaker behavior using /always-fail
• Fallback handling with createResilientFetch

Also adds CORS support to the sandbox server so browser-based examples can communicate with the local sandbox during development.

Changes

• Added a new browser example under examples/browser
• Set up a lightweight Vite + TypeScript environment
• Added a Retry Demo using /unstable-data
• Added a Circuit Breaker Demo using /always-fail
• Added browser example documentation and setup instructions
• Added CORS headers to the sandbox server to enable browser-based requests

Testing

• Started the local sandbox server
• Ran the browser example using Vite
• Verified retry behavior against /unstable-data
• Verified circuit breaker behavior against /always-fail
• Confirmed fallback responses were returned when expected
• Confirmed browser requests worked correctly after enabling CORS support

[vercel]

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[AryanSharma48]

Seem good 👍