Add OpenUI voice QA playbook article

[Bjvsquare]

Summary

• adds a written-content submission for issue Written Content: OpenUI for Voice Agents: Pairing LiveKit with Generative UI for Real-Time Visual Feedback #6
• focuses on QA for LiveKit + OpenUI voice agents: turn IDs, trace capture, stream replay, semantic validation, interruption testing, and UI action safety
• keeps the angle distinct from architecture walkthroughs by showing how to prove realtime voice plus visual feedback stays aligned

Validation

• git diff --check
• npx --yes markdownlint-cli --disable MD013 -- "Articles/OpenUI for Voice Agents - A QA Playbook for Real-Time Visual Feedback.md"
• generic filler phrase scan
• ASCII-only check

Related: #6