Optimize cover image for multi-agent workflows blog post (#2785)

Resize from 6016x4000 (33MB) to 1200x800 (1.7MB) to fix deployment issue.
Original 33MB file was 10x larger than other cover images and likely
causing webpack compilation or deployment problems.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: MaxGhenis