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>

vision.md

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+# Aether Vision
+
+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) for who we are and what we believe.
+
+## What This Is
+
+Aether is an open-source infrastructure library for building distributed, event-sourced systems in Go. It provides:
+
+- **Event sourcing primitives** - Event, EventStore interface, snapshots
+- **Event stores** - In-memory (testing) and JetStream (production)
+- **Event bus** - Local and NATS-backed pub/sub with namespace isolation
+- **Cluster management** - Node discovery, leader election, shard distribution
+- **Namespace isolation** - Logical boundaries for multi-scope deployments
+
+## Who This Serves
+
+- **Go developers** building distributed systems
+- **Teams** implementing event sourcing and CQRS patterns
+- **Projects** needing actor-based concurrency with event persistence
+
+## Goals
+
+1. **Simple event sourcing** - Clear primitives that compose well
+2. **NATS-native** - Built for JetStream, not bolted on
+3. **Horizontal scaling** - Consistent hashing, shard migration, leader election
+4. **Namespace isolation** - Logical boundaries without infrastructure overhead
+
+## Non-Goals
+
+- Opinionated multi-tenancy (product layer concern)
+- Domain-specific abstractions (use the primitives)
+- GraphQL/REST API generation (build on top)
+- UI components (see iris)