docs: Add documentation for FlatRun UI

[Lantum-Brendan]

Add docs.json manifest and 4 markdown files covering overview, development setup, connecting to agent, and production deployment.

[sourceant]

Code Review Summary

The PR introduces comprehensive documentation for the FlatRun UI, including a manifest for the documentation system and four core guides covering setup, connection, and deployment.

🚀 Key Improvements

• Added a structured manifest docs.json for integration with documentation kits.
• Provided clear Nginx and Docker deployment examples.
• Defined a clear project structure for contributors in docs/development.md.

💡 Minor Suggestions

• Standardize Nginx proxy headers to include X-Forwarded-For.
• Suggest multi-stage builds for Docker to improve reproducibility.

[sourceant]

Review complete. See the overview comment for a summary.

[sourceant]

The Nginx configuration for /api is missing the rewrite directive if the backend agent doesn't expect the /api prefix, or it may need trailing slash consistency. Also, proxy_set_header X-Forwarded-For is a standard best practice for identifying the client IP through proxies.

Suggested change

	location /api {
	location /api/ {
	proxy_pass http://localhost:8090/;
	proxy_set_header Host $host;
	proxy_set_header X-Real-IP $remote_addr;
	proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
	}

[sourceant]

The Dockerfile relies on a local dist/ folder and a nginx.conf that might not exist in the root. It is safer to suggest a multi-stage build to ensure the build environment is consistent and doesn't depend on the host machine's state.

Suggested change

	FROM nginx:alpine
	# Build stage
	FROM node:18-alpine as build-stage
	WORKDIR /app
	COPY package*.json ./
	RUN npm install
	COPY . .
	RUN npm run build
	# Production stage
	FROM nginx:stable-alpine
	COPY --from=build-stage /app/dist /usr/share/nginx/html
	EXPOSE 80
	CMD ["nginx", "-g", "daemon off;"]