feat: add simple chat for nextjs template

templates/simple/nextjs/README-template.md

templates/simple/nextjs/app/components/chat-avatar.tsx

templates/simple/nextjs/app/components/chat-history.tsx

templates/simple/nextjs/app/components/chat-item.tsx

templates/simple/nextjs/app/components/chat-section.tsx

templates/simple/nextjs/app/components/header.tsx

templates/simple/nextjs/app/components/message-form.tsx

templates/simple/nextjs/app/favicon.ico

templates/simple/nextjs/app/globals.css

templates/simple/nextjs/app/page.tsx

templates/simple/nextjs/app/services/chatStorage.service.ts

templates/simple/nextjs/public/llama.png

templates/simple/nextjs/public/next.svg

templates/simple/nextjs/public/vercel.svg