Function diagnostic_from_parse_defect 

pub fn diagnostic_from_parse_defect(defect: &ParseDefect) -> Diagnostic

Converts a parse-time defect from the template model into a full Diagnostic, sourcing severity, category, origin, and description from the rule registry. This is the single boundary where the model’s plain findings acquire reporting metadata; like RegisteredDiagnostic::build, it panics if the defect’s rule ID is not registered.