test: add e2e test for Turbopack with multiple PostCSS configs
Verifies that Turbopack correctly handles multiple postcss.config.js
files across separate directories with many CSS module files.
Test setup:
- 5 directories, each with its own postcss.config.js and plugin
- 20 CSS module files per directory (100 total)
- Custom PostCSS plugin that transforms color: red → green
- Validates all 100 elements render with correct CSS module classes
- Validates PostCSS transforms are applied in the CSS output
https://claude.ai/code/session_01VjFd6129z6XbursoXTf9g7
