Switch evaluation sessions to Jack

[Ridealist]

Summary

• Update the evaluation/free-conversation persona from Kate to Jack.
• Apply Jack-specific evaluation prompt defaults, opening sentence, metadata expectations, and TTS voice selection.
• Show Jack in the evaluation UI, including the lobby activity description, admin prompt description, and avatar image.

Testing

• cd agent && UV_CACHE_DIR=/tmp/uv-cache uv run python -m pytest tests/test_prompt_evaluation.py tests/test_realtime_metadata.py tests/test_logger.py -q
• cd client && node --test tests/evaluation-prompt-source.test.mjs tests/token-route.test.mjs tests/prompt-version-db-store.test.mjs tests/evaluation-prompt- route.test.mjs
• cd client && pnpm run build

Notes

• Practice/task sessions still use Kate.
• Evaluation sessions use Jack and /agents/jack_photo.png.