core/proposal_review/summary.py: idle_summary(root=None) -> ProposalReviewIdleSummary composes the landed scan/build_report/dry_check into one JSON-safe primitives-only value (safe, total, review_needed, malformed, by_family tuple-of-pairs, errors). Pure read — no mutation, no clock, no runtime touch. errors carries the dry-check violations (why not safe); IT-b reuses it for a captured reporter exception. 7 tests incl. read-only + deterministic + json-serializable.
