Give scheduled games random seeds

[KyleHerndon]

Summary

• default EpisodeRequest.seed to a random 31-bit nonnegative seed when omitted or explicitly null
• rely on that protocol default so all commissioners that construct EpisodeRequest normally get random seeds by default
• add coverage for protocol defaults plus baseline, self-play, rolling-window, and team-block schedules carrying valid seeds

Validation

• No lint command is defined in pyproject.toml or the GitHub workflow for this repo
• git diff --check
• timeout 30s uv run pytest tests/test_commissioner_strategies.py -q

Note: tests/test_commissioner_websocket.py currently times out locally on the first TestClient health check before any scheduling behavior is exercised.