List trusted issuers

List the issuers this tenant trusts when verifying presented credentials. During verification, Didit ID rejects any credential whose iss is not an active trusted issuer (the supply-chain-of-trust gate). The tenant's own self-trust row is guaranteed to exist so the registry is never empty. Scoped to the caller's tenant via the API key. Returns a bare JSON array ordered by most-recently-created first.