add ProxyForFree to Proxy Server section

[vsmutok]

Summary

This PR adds ProxyForFree to the Proxy Server section.

About the project

ProxyForFree is a Python-based utility and FastAPI service that simplifies setting up multiple parallel proxy servers on Linux. It routes traffic through isolated OpenVPN tunnels (using policy routing and 3proxy), allowing users to maintain multiple exit IPs for scraping or testing without paid proxy subscriptions.

• FastAPI Management: REST API and CLI to start, stop, and monitor proxies.
• Pure Routing: Policy routing via OpenVPN and 3proxy.
• Developer-friendly: Managed with uv and Makefile.

Checklist

• Added to the correct section (Proxy Server).
• Placed in alphabetical order.
• Description is objective and adheres to guidelines.