feat: scaffold frontend (Vite + React + Vitest)

- Añade scaffold de frontend con Vite y React
- Configura Vitest y tests básicos (App, Navbar)
- Añade QueryClient y hooks/plantillas iniciales

frontend/tailwind.config.cjs

@@ -0,0 +1,21 @@
+module.exports = {
+  content: ['./index.html', './src/**/*.{ts,tsx}'],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};
+module.exports = {
+  content: ['./index.html', './src/**/*.{ts,tsx}'],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};
+module.exports = {
+  content: ['./index.html', './src/**/*.{ts,tsx,js,jsx}'],
+  theme: {
+    extend: {},
+  },
+  plugins: [],
+};