20260903T1428Z prd relationships e5

What. Added requirement E5 (P0): the extractor emits relation claims with target_partial_id, typed against the relation-type registry, cross-event targets rejected at the contract boundary. Extended M1 to report relation-claim yield and precision per type, including the other label distribution.

Why. Relationship extraction ships with the extraction stage so M1 measures it before anything consumes it (D21); same designed-on-data doctrine as matching.

Verify. docs/PRD.md sections 6 (E5 row, M1 row) and the appendix link to design/relationships.md.