Streams listed in Options.Streams are created by Start() when the
embedded NATS server initializes, replacing manual EnsureStream calls
during setup. Migrates nats-chatroom and pubsub-crud examples.
Demonstrates pub/sub messaging as an alternative to custom Rooms
implementation. Uses delaneyj/toolbelt/embeddednats to run NATS
with JetStream inside the binary - no external server required.