Add LiveKit OpenUI voice agent article

[tuanadr]

Summary

• adds an issue Written Content: OpenUI for Voice Agents: Pairing LiveKit with Generative UI for Real-Time Visual Feedback #6 article on pairing LiveKit voice agents with OpenUI-rendered visual state
• frames generated UI as the voice agent's visual commit log: persistent options, forms, confirmations, stale-turn handling, and safe actions
• covers practical architecture boundaries: LiveKit for realtime audio, OpenUI for streamed visual state, and app code for authority and permissions

Validation

• git diff --check
• npx --yes markdownlint-cli "Articles/Voice Agents Need a Visual Commit Log.md" --disable MD013

Disclosure

Drafting and editing were AI-assisted. I checked the article against current OpenUI docs and the issue brief resources, and I am responsible for the final wording and technical accuracy.

Related: #6