Finish podcast creator reusable loop example

[fazpu]

Summary

• Add scheduler support for priority, run_on_start, run_after_successes, and emits_goal_check workflows.
• Add session-scoped project_state/eval_checks paths to rendered prompts and allow non-goal_check workflows to emit goal_check.json.
• Finish examples/podcast_creator with eval_reviewer, eval_runner, outer, and inner workflow configs/prompts.
• Document the new workflow fields and session-scoped state layout.

Verification

• uv run pytest
• uv run ruff check .
• uv run ruff format --check .
• uv run pyright