Parser: parse-cmd-list now skips a leading 'then' token so that
'on click from #bar then add .clicked' compiles correctly instead
of producing nil as the body.
Bootstrap tests: fix two broken tests whose assertions were
incomplete or contradictory:
- "cleanup removes event listeners" — deactivate + re-click to
verify listener is gone
- "reinitializes if script attribute changes" — actually change
the _ attribute before re-activating and re-clicking
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>