feat: add Tailwind CSS and PostCSS configuration

- Created postcss.config.js to configure PostCSS with Tailwind CSS and Autoprefixer.
- Updated svelte.config.js to enable PostCSS preprocessing.
- Added tailwind.config.js for Tailwind CSS configuration.
- Updated yarn.lock to include new dependencies for Tailwind CSS, PostCSS, and related plugins.

frontend/src/css/style.css

@@ -0,0 +1,3 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;