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.

global.css

@@ -0,0 +1,31 @@
+@import "tailwindcss/theme.css" layer(theme);
+@import "tailwindcss/preflight.css" layer(base);
+@import "tailwindcss/utilities.css";
+
+/* Platform font fallbacks so typographic scale behaves consistently. */
+@media android {
+  :root {
+    --font-sans: normal;
+    --font-serif: serif;
+    --font-mono: monospace;
+    --font-rounded: normal;
+  }
+}
+
+@media ios {
+  :root {
+    --font-sans: system-ui;
+    --font-serif: ui-serif;
+    --font-mono: ui-monospace;
+    --font-rounded: ui-rounded;
+  }
+}
+
+@layer theme {
+  @theme {
+    --color-brand-50: #f5f7ff;
+    --color-brand-100: #e9edff;
+    --color-brand-500: #4f6bd9;
+    --color-brand-700: #3147a6;
+  }
+}