Fix `hero.mp4` video loading - Vercel Blob Storage data transfer limit exceeded

[yamcodes]

Problem

The hero demo video (hero.mp4) on arkenv.js.org is failing to load with a 403 Forbidden error. The video is currently served from Vercel Blob Storage, which has hit the Hobby plan data transfer limit (13.7 GB / 10 GB).

Current URL: https://x9fkbqb4whr3w456.public.blob.vercel-storage.com/hero.mp4
Status: 403 Forbidden
Issue: Data transfer limit exceeded (access resumes on 14/11/2025)

Current Impact

• Video fails to load, showing PNG fallback instead
• Users can't see the demo video on the homepage

Recommended Solution

Migrate to Mux for video hosting:

• ✅ Purpose-built for video delivery with optimized CDN
• ✅ Better performance and reliability
• ✅ More cost-effective at scale
• ✅ Advanced features (analytics, encoding, thumbnails)

Implementation:

1. Upload hero.mp4 to Mux
2. Update VideoDemo component to use Mux playback URL
3. Configure environment variable for Mux asset ID

Reference: https://docs.mux.com/guides/video/play-your-videos