Built standalone PromptEditor with transparent-textarea overlay for syntax
highlighting of Jinja2 expressions, statements, and comments. Includes
clickable variable sidebar for insertion and preview panel with sample data
substitution. Integrated into ExperimentPage PipelineStageCard. 27 tests added.
- Full setup form with username, password, confirm password
- Auth detection on mount (redirects if already authenticated)
- Client-side validation (empty username, short password, mismatch)
- Server error handling (409 conflict, network errors)
- Welcoming UI with gradient background, dark mode support
- 9 new tests covering all states and error paths
- Updated App.test.tsx to handle async SetupPage rendering
- Added @testing-library/user-event dependency
