fix: replace tailwind.config.ts with .js for PostCSS compatibility

Tailwind v3 PostCSS plugin doesn't load TypeScript config files,
resulting in empty CSS output (no utility classes generated).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tailwind.config.js

@@ -1,10 +1,10 @@
 /** @type {import('tailwindcss').Config} */
-export default {
-  content: ['./index.html', './src/**/*.{js,jsx}'],
+module.exports = {
+  content: ['./src/**/*.{ts,tsx}'],
   theme: {
     extend: {
       fontFamily: {
-        sans: ['Manrope', 'sans-serif'],
+        sans: ['var(--font-manrope)', 'sans-serif'],
       },
       colors: {
         brand: {