fix: document turbot download body.on streaming bug and workaround (#63)

[vkumbha]

Summary

• Documents the turbot download failure (body.on is not a function) affecting v1.32.x and v1.33.x in a new Troubleshooting section of the README
• Provides a NODE_OPTIONS workaround so users can download mods immediately without waiting for a CLI patch
• Includes the exact one-liner source fix (Readable.fromWeb()) for CLI maintainers to apply in the private source repo

Root Cause (for CLI maintainers)

The download implementation calls .on('data', ...) on the response body returned by native fetch(). In Node.js 18+, fetch() returns a Web ReadableStream (which has no .on()), not the Node.js stream.Readable that node-fetch used to return. The fix is a one-liner:

// Before:
const re = await fetch(url);
re.body.on('data', chunk => fileStream.write(chunk));  // ❌ TypeError

// After:
import { Readable } from 'node:stream';
import { pipeline } from 'node:stream/promises';
const re = await fetch(url);
await pipeline(Readable.fromWeb(re.body), fileStream);  // ✅

Test plan

• Verified bug reproduction on CLI v1.32.0-rc.1 and v1.33.0-rc.8 (Darwin/amd64)
• Confirmed NODE_OPTIONS workaround successfully captures the S3 URL and curl downloads the zip
• Confirmed downloaded zip (@turbot/aws-lambda@5.19.1, 39 MB) is valid and deploys successfully via turbot up --zip-file

Closes #63

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