Function build_proxy_url 

pub fn build_proxy_url(host: Option<&str>, s: &Settings) -> Option<String>

Build the URL for a proxy hostname: a legacy slug, or an automatic <daemon>.<worktree>.<project> host.

This is the one place a pitchfork URL is spelled out, so everything that shows a URL, injects PITCHFORK_URL, or renders a template agrees with what the proxy serves.

Returns None if:

• host is None (not proxied)
• Proxy is disabled in settings
• proxy.port is invalid (out of range or zero)