com.publicdomainrelay.temp.market.registerBidder

Register a bidder with the market registry. Called by bidders after they publish a bidderDiscovery record in their own repo and connect to the relay. The registry verifies the caller's service-auth JWT issuer matches the bidderDid, then indexes the bidder so it appears in listBidders queries. Liveness is determined by the registry polling the bidder's bidderDiscovery record — there is no separate heartbeat procedure.