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.

.vscode/settings.json

@@ -26,5 +26,8 @@
     "i18n-ally.keystyle": "nested",
     "[svelte]": {
         "editor.defaultFormatter": "svelte.svelte-vscode"
+    },
+    "files.associations": {
+        "css": "tailwindcss"
     }
 }