Deepyn Dixies staging

Development-only authenticated staging slices. Use the same disposable Supabase project and test accounts.

1. ProjectsSign in, list private projects, and create a project.2. WorkspaceLoad and save a private draft with revision checks.3. Version historyCreate and review append-only snapshots.4. Private filesUpload project-scoped files within the 100 MB limit.

Live smoke testing begins only after staging deployment.