Optimize KV usage to reduce Cloudflare operations

Fix admin panel visibility and KV storage bug

Fix message flickering: incremental rendering instead of full re-render

Remove message animation to prevent flickering on poll updates

Update theme: modern black & white design with subtle message colors

Major UI upgrade: Dark glassmorphism theme + Admin panel

Add admin status check via KV storage

Add server-side anti-spam protection

Add IP ban functionality

Add message length limit (2000 chars) and improve polling

Fix API routing and contact add functionality

Fix user search - correct key filtering in KV list

Add local dev server with API proxy

Remove duplicate frontend files from root

Fix API endpoint routing and error handling