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/index.ts

@@ -1,3 +1,4 @@
+import "./css/style.css"
 import App from "./App.svelte"
 import { hydrate } from "svelte"