Refactor nginx.conf: clarity, best practices, and correct Cloudflare IP forwarding

[engine-labs-paul]

Summary

This PR refactors the nginx.conf file for greater clarity, simplicity, and correctness, ensuring proper end-user IP forwarding in a Render.com environment with Cloudflare as a proxy.

Details

• Rewrote and expanded comments throughout to explain the configuration and goals clearly.
• Updated and expanded Cloudflare IP range list (IPv4 and IPv6) with references.
• Trusted Render.com's internal network for correct IP relay in multi-proxy hops.
• Explicit use of real_ip_header CF-Connecting-IP with real_ip_recursive on for best Cloudflare/Nginx compatibility.
• Used a map for $client_ip to ensure accurate user IP forwarding in headers.
• Factored and reordered common proxy headers to reduce repetition and improve maintainability.
• Centralized debug logging and improved log format.
• Simplified each location block, retaining only necessary proxy configuration.
• Added .gitignore (exclude temp/cache files and common artifacts).
• All functionality is preserved; only readability, maintainability, and standards improved.

Warning: Task VM test is not passing, Engine will perform much better if you fix the setup