feat: adds app shell, design system, and theme support for M0

fix: restore toast import in DashboardApp

fix: adds missing fmt import to router.go

feat: implements ATProto auth provider infrastructure (M4)

feat: adds connector-agnostic API routes and handlers for documents and connections

feat: adds classic editor view with CodeMirror and live preview

fix: restore toast import in DashboardApp

docs: updates docs