Function render 

pub fn render(
    grids: &MetricGrids<'_>,
    roles: &ResolvedRoles,
    findings: &[Finding],
    clip_filter: Option<&str>,
) -> String

Render report HTML from shared metric pose grids.

clip_filter restricts the report to one clip name when present. The function performs no filesystem I/O and cannot report write errors; callers choose where to store or serve the returned self-contained HTML string.