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.

CONTAINER-DIAGRAM.mmd

@@ -0,0 +1,123 @@
+%% C4 Container Diagram - Level 2
+%% DaviesTechLabs Homelab AI/ML Platform
+%%
+%% To render: Use Mermaid Live Editor or VS Code Mermaid extension
+
+graph TB
+    subgraph users["Users"]
+        user["👤 User"]
+    end
+
+    subgraph ingress["Ingress Layer"]
+        cloudflared["cloudflared<br/>(Tunnel)"]
+        envoy["Envoy Gateway<br/>(HTTPRoute)"]
+    end
+
+    subgraph frontends["Frontend Applications"]
+        companions["Companions WebApp<br/>[Go + HTMX]<br/>AI Chat Interface"]
+        voice["Voice WebApp<br/>[Gradio]<br/>Voice Assistant UI"]
+        kubeflow_ui["Kubeflow UI<br/>[React]<br/>Pipeline Management"]
+    end
+
+    subgraph messaging["Message Bus"]
+        nats["NATS<br/>[JetStream]<br/>Event Streaming"]
+    end
+
+    subgraph handlers["NATS Handlers"]
+        chat_handler["Chat Handler<br/>[Python]<br/>RAG + LLM Orchestration"]
+        voice_handler["Voice Assistant<br/>[Python]<br/>STT → LLM → TTS"]
+        pipeline_bridge["Pipeline Bridge<br/>[Python]<br/>Workflow Triggers"]
+    end
+
+    subgraph ai_services["AI Services (KServe)"]
+        whisper["Whisper<br/>[faster-whisper]<br/>Speech-to-Text"]
+        xtts["XTTS<br/>[Coqui]<br/>Text-to-Speech"]
+        vllm["vLLM<br/>[ROCm]<br/>LLM Inference"]
+        embeddings["BGE Embeddings<br/>[sentence-transformers]<br/>Vector Encoding"]
+        reranker["BGE Reranker<br/>[sentence-transformers]<br/>Document Ranking"]
+    end
+
+    subgraph storage["Data Stores"]
+        milvus["Milvus<br/>[Vector DB]<br/>RAG Storage"]
+        valkey["Valkey<br/>[Redis API]<br/>Session Cache"]
+        postgres["CloudNative-PG<br/>[PostgreSQL]<br/>Metadata"]
+        minio["MinIO<br/>[S3 API]<br/>Object Storage"]
+    end
+
+    subgraph workflows["Workflow Engines"]
+        argo["Argo Workflows<br/>[DAG Engine]<br/>Complex Pipelines"]
+        kfp["Kubeflow Pipelines<br/>[ML Platform]<br/>Training + Inference"]
+        argo_events["Argo Events<br/>[Event Source]<br/>NATS → Workflow"]
+    end
+
+    subgraph mlops["MLOps"]
+        mlflow["MLflow<br/>[Tracking Server]<br/>Experiment Tracking"]
+        volcano["Volcano<br/>[Scheduler]<br/>GPU Scheduling"]
+    end
+
+    %% User flow
+    user --> cloudflared
+    cloudflared --> envoy
+    envoy --> companions
+    envoy --> voice
+    envoy --> kubeflow_ui
+
+    %% Frontend to NATS
+    companions --> |WebSocket| nats
+    voice --> |HTTP/WS| nats
+
+    %% NATS to handlers
+    nats --> chat_handler
+    nats --> voice_handler
+    nats --> pipeline_bridge
+
+    %% Handlers to AI services
+    chat_handler --> embeddings
+    chat_handler --> reranker
+    chat_handler --> vllm
+    chat_handler --> milvus
+    chat_handler --> valkey
+
+    voice_handler --> whisper
+    voice_handler --> embeddings
+    voice_handler --> reranker
+    voice_handler --> vllm
+    voice_handler --> xtts
+
+    %% Pipeline flow
+    pipeline_bridge --> argo_events
+    argo_events --> argo
+    argo_events --> kfp
+    kubeflow_ui --> kfp
+
+    %% Workflow to AI
+    argo --> ai_services
+    kfp --> ai_services
+    kfp --> mlflow
+
+    %% Storage connections
+    ai_services --> minio
+    milvus --> minio
+    kfp --> postgres
+    mlflow --> postgres
+    mlflow --> minio
+
+    %% GPU scheduling
+    volcano -.-> vllm
+    volcano -.-> whisper
+    volcano -.-> xtts
+
+    %% Styling
+    classDef frontend fill:#90EE90,stroke:#333
+    classDef handler fill:#87CEEB,stroke:#333
+    classDef ai fill:#FFB6C1,stroke:#333
+    classDef storage fill:#DDA0DD,stroke:#333
+    classDef workflow fill:#F0E68C,stroke:#333
+    classDef messaging fill:#FFA500,stroke:#333
+    
+    class companions,voice,kubeflow_ui frontend
+    class chat_handler,voice_handler,pipeline_bridge handler
+    class whisper,xtts,vllm,embeddings,reranker ai
+    class milvus,valkey,postgres,minio storage
+    class argo,kfp,argo_events,mlflow,volcano workflow
+    class nats messaging