fix: issue of prompt enhancer not working in prod mode

[akashMishraX]

For issue #1448, this is my PR.

Issue Found:

The enhanced prompt was working in development mode because Node.js can handle a text stream. However, in production (Cloudflare Workers environment), it was failing.

Main Error:

The error "This ReadableStream did not return bytes" occurred because Cloudflare Workers expect a byte-based ReadableStream (e.g., Uint8Array). If _streamText (in stream-text.ts) returns a text-based stream or a different format, it fails in workerd.

Solution:

I updated api.enhancer.ts by implementing returnStream, which creates a new byte-based ReadableStream and returns it as the API response. I tested this fix in production mode, and it is now working correctly.

Thank you for reading!