feat: add comprehensive architecture documentation

- Add AGENT-ONBOARDING.md for AI agents
- Add ARCHITECTURE.md with full system overview
- Add TECH-STACK.md with complete technology inventory
- Add DOMAIN-MODEL.md with entities and bounded contexts
- Add CODING-CONVENTIONS.md with patterns and practices
- Add GLOSSARY.md with terminology reference
- Add C4 diagrams (Context and Container levels)
- Add 10 ADRs documenting key decisions:
  - Talos Linux, NATS, MessagePack, Multi-GPU strategy
  - GitOps with Flux, KServe, Milvus, Dual workflow engines
  - Envoy Gateway
- Add specs directory with JetStream configuration
- Add diagrams for GPU allocation and data flows

Based on analysis of homelab-k8s2 and llm-workflows repositories
and kubectl cluster-info dump data.

decisions/0003-use-nats-for-messaging.md

@@ -0,0 +1,112 @@
+# Use NATS for AI/ML Messaging
+
+* Status: accepted
+* Date: 2025-12-01
+* Deciders: Billy Davies
+* Technical Story: Selecting message bus for AI service orchestration
+
+## Context and Problem Statement
+
+The AI/ML platform requires a messaging system for:
+- Real-time chat message routing
+- Voice request/response streaming
+- Pipeline triggers and status updates
+- Event-driven workflow orchestration
+
+We need a messaging system that handles both ephemeral real-time messages and persistent streams.
+
+## Decision Drivers
+
+* Low latency for real-time chat/voice
+* Persistence for audit and replay
+* Simple operations for homelab
+* Support for request-reply pattern
+* Wildcard subscriptions for routing
+* Binary message support (audio data)
+
+## Considered Options
+
+* Apache Kafka
+* RabbitMQ
+* Redis Pub/Sub + Streams
+* NATS with JetStream
+* Apache Pulsar
+
+## Decision Outcome
+
+Chosen option: "NATS with JetStream", because it provides both fire-and-forget messaging and persistent streams with significantly simpler operations than alternatives.
+
+### Positive Consequences
+
+* Sub-millisecond latency for real-time messages
+* JetStream provides persistence when needed
+* Simple deployment (single binary)
+* Excellent Kubernetes integration
+* Request-reply pattern built-in
+* Wildcard subscriptions for flexible routing
+* Low resource footprint
+
+### Negative Consequences
+
+* Less ecosystem than Kafka
+* JetStream less mature than Kafka Streams
+* No built-in schema registry
+* Smaller community than RabbitMQ
+
+## Pros and Cons of the Options
+
+### Apache Kafka
+
+* Good, because industry standard for streaming
+* Good, because rich ecosystem (Kafka Streams, Connect)
+* Good, because schema registry
+* Good, because excellent for high throughput
+* Bad, because operationally complex (ZooKeeper/KRaft)
+* Bad, because high resource requirements
+* Bad, because overkill for homelab scale
+* Bad, because higher latency for real-time messages
+
+### RabbitMQ
+
+* Good, because mature and stable
+* Good, because flexible routing
+* Good, because good management UI
+* Bad, because AMQP protocol overhead
+* Bad, because not designed for streaming
+* Bad, because more complex clustering
+
+### Redis Pub/Sub + Streams
+
+* Good, because simple
+* Good, because already might use Redis
+* Good, because low latency
+* Bad, because pub/sub not persistent
+* Bad, because streams API less intuitive
+* Bad, because not primary purpose of Redis
+
+### NATS with JetStream
+
+* Good, because extremely low latency
+* Good, because simple operations
+* Good, because both pub/sub and persistence
+* Good, because request-reply built-in
+* Good, because wildcard subscriptions
+* Good, because low resource usage
+* Good, because excellent Go/Python clients
+* Bad, because smaller ecosystem
+* Bad, because JetStream newer than Kafka
+
+### Apache Pulsar
+
+* Good, because unified messaging + streaming
+* Good, because multi-tenancy
+* Good, because geo-replication
+* Bad, because complex architecture
+* Bad, because high resource requirements
+* Bad, because smaller community
+
+## Links
+
+* [NATS.io](https://nats.io)
+* [JetStream Documentation](https://docs.nats.io/nats-concepts/jetstream)
+* Related: [ADR-0004](0004-use-messagepack-for-nats.md) - Message format