Add PostCSS configuration and skills lock file

- Created a new PostCSS configuration file to integrate Tailwind CSS.
- Added a skills lock file containing various Expo skills with their respective source and computed hashes.

postcss.config.mjs

@@ -0,0 +1,5 @@
+export default {
+  plugins: {
+    '@tailwindcss/postcss': {},
+  },
+};