This migration aligns the D1 database schema with the unified Ed25519
authentication system that replaced the dual peerId/secret system.
Changes:
- Renames peer_id to username in offers table
- Renames answerer_peer_id to answerer_username in offers table
- Renames peer_id to username in ice_candidates table
- Adds service_fqn column to offers table
- Updates all indexes and foreign keys
