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>

CLAUDE.md

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+# Aether
+
+Distributed actor system with event sourcing for Go, powered by NATS.
+
+## Organization Context
+
+This repo is part of Flowmade. See:
+- [Organization manifesto](../architecture/manifesto.md) - who we are, what we believe
+- [Repository map](../architecture/repos.md) - how this fits in the bigger picture
+- [Vision](./vision.md) - what this specific product does
+
+## Setup
+
+```bash
+git clone git@git.flowmade.one:flowmade-one/aether.git
+cd aether
+go mod download
+```
+
+Requires NATS server for integration tests:
+```bash
+# Install NATS
+brew install nats-server
+
+# Run with JetStream enabled
+nats-server -js
+```
+
+## Project Structure
+
+```
+aether/
+├── event.go           # Event, ActorSnapshot, EventStore interface
+├── eventbus.go        # EventBus, EventBroadcaster interface
+├── nats_eventbus.go   # NATSEventBus - cross-node event broadcasting
+├── store/
+│   ├── memory.go      # InMemoryEventStore (testing)
+│   └── jetstream.go   # JetStreamEventStore (production)
+├── cluster/
+│   ├── manager.go     # ClusterManager
+│   ├── discovery.go   # NodeDiscovery
+│   ├── hashring.go    # ConsistentHashRing
+│   ├── shard.go       # ShardManager
+│   ├── leader.go      # LeaderElection
+│   └── types.go       # Cluster types
+└── model/
+    └── model.go       # EventStorming model types
+```
+
+## Development
+
+```bash
+make build    # Build the library
+make test     # Run tests
+make lint     # Run linters
+```
+
+## Architecture
+
+### Event Sourcing
+
+Events are the source of truth. State is derived by replaying events.
+
+```go
+// Create an event
+event := &aether.Event{
+    ID:        uuid.New().String(),
+    EventType: "OrderPlaced",
+    ActorID:   "order-123",
+    Version:   1,
+    Data:      map[string]interface{}{"total": 100.00},
+    Timestamp: time.Now(),
+}
+
+// Persist to event store
+store.SaveEvent(event)
+
+// Replay events to rebuild state
+events, _ := store.GetEvents("order-123", 0)
+```
+
+### Namespace Isolation
+
+Namespaces provide logical boundaries for events and subscriptions:
+
+```go
+// Subscribe to events in a namespace
+ch := eventBus.Subscribe("tenant-abc")
+
+// Events are isolated per namespace
+eventBus.Publish("tenant-abc", event)  // Only tenant-abc subscribers see this
+```
+
+### Clustering
+
+Aether handles node discovery, leader election, and shard distribution:
+
+```go
+// Create cluster manager
+manager := cluster.NewClusterManager(natsConn, nodeID)
+
+// Join cluster
+manager.Start()
+
+// Leader election happens automatically
+if manager.IsLeader() {
+    // Coordinate shard assignments
+}
+```
+
+## Key Patterns
+
+- **Events are immutable** - Never modify, only append
+- **Snapshots for performance** - Periodically snapshot state to avoid full replay
+- **Namespaces for isolation** - Not multi-tenancy, just logical boundaries
+- **NATS for everything** - Events, pub/sub, clustering all use NATS