[P1 governance] Twin map accepts overlapping, stale, duplicate, and wrong-arity registry entries

[bhelm]

Confirmed gap

The checked-in parity twin map is used as inventory truth, but current validation does not fully reject pair↔unpaired overlap, stale function/property entries, duplicate targets, or exact-arity mismatches. Concrete stale/wrong mappings include collapseOverCount/4 -> collapsedCoverage/3, stale analyzeDay/30, and stale rank/1 inventory entries.

Acceptance

• Validate pair↔unpaired disjointness for files, functions, and properties.
• Reject stale sides, duplicate targets, and non-exact function arity.
• Correct the concrete stale/wrong entries without regenerating away curated mappings/evidence.
• Add red-first tests for each invariant and keep the repository ledger green.

Tracks tooling/map metadata only; no production behavior change.