Three spec-bug fixes from T10 implementation:
- Match.claim_id: drop UNIQUE constraint (T4 schema error) — reversals add a 2nd row per claim (audit trail). Add explicit non-unique index ix_matches_claim_id to preserve query performance. Mirrored in ORM and migration 0001_initial.sql.
- test_run_orphan_remit_leaves_claim_unmatched: claim PCN-A does not match remit PCN-NEW, so unmatched_claims must be 1, not 0.
- test_run_reversal_flips_paid_to_reversed: claim service_date_from was 9 days before reversal remit service_date (outside default 7-day window) so no match occurred; changed to 5 days apart so match() picks the claim.
- test_match_unique_per_claim: in test_db_models.py asserted the now-removed UNIQUE behavior; renamed and inverted to assert the audit-trail design (two Match rows per claim allowed).
Tyler