feat: add @nuxtjs/color-mode module and configure color preferences

nuxt.config.ts

@@ -5,6 +5,7 @@ export default defineNuxtConfig({
   compatibilityDate: "2025-07-15",
   devtools: { enabled: true },
   css: ["./app/assets/css/main.css"],
+  modules: ["@nuxtjs/color-mode"],
   vite: {
     plugins: [tailwindcss()],
   },
@@ -19,5 +20,10 @@ export default defineNuxtConfig({
       firebaseMeasurementId: process.env.NUXT_PUBLIC_FIREBASE_MEASUREMENT_ID,
       backendUrl: process.env.NUXT_PUBLIC_BACKEND_URL || 'http://localhost:3000'
     }
+  },
+  colorMode: {
+    preference: 'light',
+    fallback: 'light',
+    classSuffix: ''
   }
 });