[server] AI Chat production UI upgrade

[Leo-learner]

What changed

• imports the aichatupdated.tar.gz server build onto a dedicated production branch
• refreshes the chat-only UI, responsive behavior, settings dialog, and profile update flow
• adds server-only branch and deployment documentation
• vendors browser-safe Markdown assets and removes the incompatible CommonJS highlight runtime

Production scope

This branch is only for aichat.dkz12345.com on the Azure server. It must preserve the server existing .env, providers.json, data/, and runtime configuration during deployment.

Validation

• npm run check
• npm run build
• APP_MODE=server-chat-only CONTROL_AUTO_START=false SERVE_DIST=1 npm run smoke:startup
• temporary-database register/login/profile-change flow
• disabled control/Finder/terminal boundary checks
• Playwright desktop and mobile UI checks with no overflow
• browser console clean after removing the incompatible highlight.js bundle