031-references-non-owning-paths

`references` seeds no implementing path: closing the C-001 ownership leak

The contract says `references` is the only non-owning edge and that the coupling gate ignores it. The indexer did not implement that. It seeded a spec's `implementingPaths` from every resolved unit location, owning or not, so a file a spec merely cited became a file it claimed. Every consumer reads that field as a claim: `couple.rs` treats a listed path as whole-file ownership, the indexer's own `owners_of_unit` does the same, and `orphaned_specs` and coverage read a non-empty list as "this spec claims something". One wrong seed made all of them wrong together. The observable defect is that a spec could not edit its own `spec.md` without a waiver once any other spec referenced it: on this corpus, changing `specs/094-one-gate-and-the-boundaries-it-holds/spec.md` was refused as `C-001` with `022-index-sharding`, which only cites it, named as the sole owner. This spec filters the seed by the `ownership` flag the loop already holds, at the single source rather than at each consumer. The citation is not lost: it stays in `resolvedUnits` with `ownership: false`, so provenance is preserved and only the ownership view changes. No DTO or schema shape changes.