Remove duplicate chat widget render from App

[mainuddinMains]

Description

Remove the extra ChatWidget render from frontend/src/App.tsx and rely on the chat UI already managed by Header.

Why

App.tsx was still rendering the standalone chat widget after chat state and handlers had already been wired into Header, which left the UI duplicated.

What changed

• Removed the ChatWidget import from frontend/src/App.tsx
• Passed chat messages, input state, send handler, and loading state into Header
• Removed the standalone ChatWidget render at the bottom of App

Validation

• npm run build