fix: resolve 502 error on project download (Fixes #3746)

[Nixxx19]

Fixes #3746

Problem

The downloadProjectAsZip function was calling buildZip without awaiting it, causing a 502 Bad Gateway error when downloading projects. This led to:

• Unhandled promise rejections if buildZip threw errors
• No timeout on S3 file fetches, causing requests to hang indefinitely
• Race conditions when clients disconnected before completion

Changes Made

• Added await to buildZip call in downloadProjectAsZip to ensure errors are properly caught and the function waits for completion before responding
• Added 30-second timeout to axios requests when fetching files from S3 to prevent hanging requests
• Improved error handling by checking res.headersSent before sending error responses to avoid crashes on client disconnects
• Enhanced error logging with more descriptive error messages for better debugging

Testing

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines

[Nixxx19]

download.issue.fix.mov

Video Demonstration

I've included a video showing the download functionality working correctly after the fix:

✅ Before the fix: Downloads would hang for ~1 minute and then show a 502 Bad Gateway error
✅ After the fix: Downloads complete successfully and the zip file is generated properly

The video shows:

• A p5.js sketch being downloaded
• The download completing successfully
• The zip file (clock_2025_12_30_16_13_37.zip, 5.2 MB) being saved without errors

This confirms that the changes resolve issue #3746.