Initial aether repository structure

Distributed actor system with event sourcing for Go:
- event.go - Event, ActorSnapshot, EventStore interface
- eventbus.go - EventBus, EventBroadcaster for pub/sub
- nats_eventbus.go - NATS-backed cross-node event broadcasting
- store/ - InMemoryEventStore (testing), JetStreamEventStore (production)
- cluster/ - Node discovery, leader election, shard distribution
- model/ - EventStorming model types

Extracted from arcadia as open-source infrastructure component.

Co-Authored-By: Claude <noreply@anthropic.com>

go.mod

@@ -0,0 +1,16 @@
+module git.flowmade.one/flowmade-one/aether
+
+go 1.23
+
+require (
+	github.com/google/uuid v1.6.0
+	github.com/nats-io/nats.go v1.37.0
+)
+
+require (
+	github.com/klauspost/compress v1.17.2 // indirect
+	github.com/nats-io/nkeys v0.4.7 // indirect
+	github.com/nats-io/nuid v1.0.1 // indirect
+	golang.org/x/crypto v0.18.0 // indirect
+	golang.org/x/sys v0.16.0 // indirect
+)