Add an exported block registry (keywords, search, insertBlock) consumed by
BlocksPanel, a NoticeProvider/NoticeHost toast stack, a guarded localStorage
prefs helper, a ProjectExtras store persisted as project.json 'extras', and a
CanvasOverlays mount point.
Refs #38
Refs #41
Refs #49
Refs #48
Refs #57
Refs #58
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
