- Redesign PreJoin component and CSS for improved template compatibility and deterministic rendering
- Remove mock studio toggle and related runtime logic; update useStudioLauncher to always use real backend
- Add README-MOCK.md to document mock studio deprecation
- Add mock-studio.html for manual popup emulation
- Update environment variable resolution in route.ts for backend API
- Add visual regression test scripts (capture, compare, visual_test_prejoin) using Playwright, Puppeteer, pixelmatch, and pngjs
- Update package.json scripts and devDependencies for visual testing
- Simplify PreJoin.stories.tsx for robust Storybook usage
