cnkang/nginx-markdown-for-agents

# Technical Summary Converts HTML to Markdown on-the-fly at the reverse proxy layer using content negotiation, allowing the same NGINX upstream to serve token-efficient Markdown to AI agents while keeping HTML for browsers unchanged. Includes User-Agent targeting so bots receive Markdown automatically via NGINX header rewriting, even without explicit `Accept: text/markdown` requests. Built as a Rust-powered NGINX module with configurable per-location control, fail-open safety, size limits, timeouts, and cache-aware variant handling (`Vary: Accept`, conditional ETags).