- Add `AuthorityDiscoveryService` (`opencontractserver/enrichment/services/authority_discovery_service.py`): registry-driven orchestrator that selects a public-domain provider, fetches statute text, bootstraps an authority corpus, and runs an equivalence-aware cross-corpus relink so act-section citations (e.g. `exchange-act:10(b)`) upgrade from `EXTERNAL` to `RESOLVED` once the corresponding USC document lands.
- Extend `find_authority_target` (`opencontractserver/enrichment/authorities.py`) with an `AuthorityKeyEquivalence` hop so subsection act-section citations (e.g. `exchange-act:10(b)`) resolve to the equivalent USC document (e.g. `usc-15:78j`) in a single call.
- Add curated Exchange Act and Securities Act ↔ USC-15 equivalence seed (`opencontractserver/enrichment/data/authority_key_equivalence_seed.py`) with 19 verified pairs, applied via data migration `0087_seed_authority_key_equivalence`.
