Generate a JSON-ready report of every per-SceneModel inspection result attached to a ModelConverterResult. Returns null when the conversion didn't run inspection (no inspect block on the pipeline) — the CLI's reporter dispatcher treats null as "nothing to write".

Per-SceneModel InspectionReport / ApplyFixesResult objects are converted with inspectionReportToJson / applyFixesResultToJson so the final blob is JSON.stringify-safe (no Map / class instances).