Render structured worker output readably

[nathanwhit]

Summary

• decode structured Codex worker events when they arrive in payload.text instead of only payload.raw
• summarize MCP tool calls, including large GitHub search results, and keep arguments/results collapsed behind details
• restore target labels/accessibility names on steering and question forms so users can see exactly what they are steering

Validation

• npm run test -- LiveSessionPanel
• npm run test
• npm run build