Paired terminal agents and early sandbox setup

What changed

• A question can now grant Claude Code and Codex together. The candidate gets a tab for each, and a turn keeps running in whichever one they are not looking at.
• Sandboxed questions now set up in the background, starting while the candidate reads the pre-assessment instructions. Claude Code and Codex no longer stop partway through writing a long file.
• In recruiter onboarding, the company website summary now appears in the first step, before the workspace is created. Editing an earlier copilot message now stops the reply in progress.