...ilwind schematic
The tailwind schematic's stylesheet injection logic has been updated to support a wider range of project configurations. Previously, it assumed a `styles.css` file was always present, which could cause issues in projects using CSS preprocessors like Sass/SCSS.
This change introduces the following logic:
- Detects if a global CSS file already exists to add the Tailwind import.
- Creates a new `tailwind.css` file if no global CSS file is found.
- Updates the build configuration in `angular.json` to include the new `tailwind.css` file.
- Updates the `styles` array in all build configurations (`production`, `development`, etc.) to ensure Tailwind is included in all builds.
- Ensures the schematic is idempotent by checking for existing Tailwind imports before adding a new one.
These changes make the schematic more robust and provide a better user experience for a wider variety of project setups.

... tailwind schematic
The Tailwind schematic now intelligently handles existing PostCSS configurations.
Instead of unconditionally creating a new `.postcssrc.json` file, the schematic now searches for `postcss.config.json` or `.postcssrc.json` in both the workspace and project roots. If an existing configuration file is found, it is updated with the required `@tailwindcss/postcss` plugin. A new configuration file is only created if one does not already exist.
This prevents conflicts and makes the schematic safer to use in projects that already have a customized PostCSS setup.

The tests for the Tailwind schematic have been refactored to improve readability and reduce boilerplate code.
Helper functions (`createTestApp`, `getWorkspace`) have been introduced to handle the repetitive setup of the test application and the parsing of the workspace configuration. The existing tests were updated to use these new helpers, making them more concise and easier to maintain.