Db now embeds IndexerDb/StreamDb/JetstreamDb/RelayDb (declared in db/keyspaces.rs, the single place mode keyspaces live) behind one cfg each, instead of 17 cfg'd fields sprinkled through the struct, open, and compact. each group owns its keyspace options, post-migration init (sequence/watermark seeding), and compaction targets. ~200 callsites renamed to the grouped paths (db.indexer.records, db.stream.events, db.jetstream.tx, db.relay.next_seq, ...).