Function render_html 

pub fn render_html(report: &SelfTestReport, audit: Option<&Value>) -> String

Render a complete HTML report for the given self-test report. audit is an optional SpecAuditReport-shaped JSON value — when present, an audit section is appended. We accept &serde_json::Value rather than the strongly-typed SpecAuditReport to keep this module decoupled from spec_audit (which lives on a separate in-flight branch).