Add profile icon and sync favicon to match

assets/icon.png — 1080×1080 social profile icon: red PLOTFLOW asterisk
on dark ink ground, full-bleed and circle-safe for Instagram cropping.
favicon.svg tuned to the same asterisk proportions so tab, OG card, and
profile avatar share one identical mark.

https://claude.ai/code/session_01VhWRYXbuqapZ9YkvksroaS

Author: claude