New events with structured payloads:
change({ markdown, html })
Fires on every content edit.
save({ markdown, html })
Fires when editor.save() is called. Consumer handles persistence.
modeChange({ current, previous })
Fires on VIEW/EDIT/WYSIWYG transitions.
themeChange({ current, previous })
Fires when themes.set() switches the active theme.
ready({ markdown, html, mode, theme })
Fires after editor.run() completes first render.
Events can be registered in the constructor via the 'on' setting
or at any time via editor.on(event, callback) / editor.off().
202/202 tests passing.
