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.

CONTEXT-DIAGRAM.mmd

@@ -0,0 +1,69 @@
+%% C4 Context Diagram - Level 1
+%% DaviesTechLabs Homelab System Context
+%%
+%% To render: Use Mermaid Live Editor or VS Code Mermaid extension
+
+graph TB
+    subgraph users["External Users"]
+        dev["👤 Developer<br/>(Billy)"]
+        family["👥 Family Members"]
+        agents["🤖 AI Agents"]
+    end
+
+    subgraph external["External Systems"]
+        cf["☁️ Cloudflare<br/>DNS + Tunnel"]
+        gh["🐙 GitHub<br/>Source Code"]
+        ghcr["📦 GHCR<br/>Container Registry"]
+        hf["🤗 Hugging Face<br/>Model Registry"]
+    end
+
+    subgraph homelab["🏠 DaviesTechLabs Homelab"]
+        direction TB
+        
+        subgraph apps["Application Layer"]
+            companions["💬 Companions<br/>AI Chat"]
+            voice["🎤 Voice Assistant"]
+            media["🎬 Media Services<br/>(Jellyfin, *arr)"]
+            productivity["📝 Productivity<br/>(Nextcloud, Gitea)"]
+        end
+        
+        subgraph platform["Platform Layer"]
+            k8s["☸️ Kubernetes Cluster<br/>Talos Linux"]
+        end
+        
+        subgraph ai["AI/ML Layer"]
+            inference["🧠 Inference Services<br/>(vLLM, Whisper, XTTS)"]
+            workflows["⚙️ Workflow Engines<br/>(Kubeflow, Argo)"]
+            vectordb["📚 Vector Store<br/>(Milvus)"]
+        end
+    end
+
+    %% User interactions
+    dev --> |manages| productivity
+    dev --> |develops| k8s
+    family --> |uses| media
+    family --> |chats| companions
+    agents --> |queries| inference
+
+    %% External integrations
+    cf --> |routes traffic| apps
+    gh --> |GitOps sync| k8s
+    ghcr --> |pulls images| k8s
+    hf --> |downloads models| inference
+
+    %% Internal relationships
+    apps --> platform
+    ai --> platform
+    companions --> inference
+    voice --> inference
+    workflows --> inference
+    inference --> vectordb
+
+    %% Styling
+    classDef external fill:#f9f,stroke:#333,stroke-width:2px
+    classDef homelab fill:#bbf,stroke:#333,stroke-width:2px
+    classDef user fill:#bfb,stroke:#333,stroke-width:2px
+    
+    class cf,gh,ghcr,hf external
+    class companions,voice,media,productivity,k8s,inference,workflows,vectordb homelab
+    class dev,family,agents user