Choreograph: fix sync row commands, sync participant race, add castName scope var

- sync delay rows now queue their commands into the next chunk (fire after sync resolves)
- sync rows without commands still work as pure barriers
- Fix sync participant race: track childrenSeen flag to handle fast child completion
- Fix sync participant: wait for children to appear before giving up (async load)
- Add castName to expression scope (available in delay/when/command templates)
- chaining-and-recursion tutorial: use , clean 2-row ritual pattern
- Remove all debug logging