Refactor app.vue and [slug].vue: add scoped styles and optimize i18n usage

app/app.vue

@@ -17,7 +17,7 @@ useHead({
   </UApp>
 </template>
 
-<style>
+<style scoped>
 body {
   font-family: 'DM Sans', sans-serif;
 }

app/assets/css/main.css

@@ -1,4 +1,8 @@
 @import "tailwindcss";
 @import "@nuxt/ui";
 
-@plugin "@tailwindcss/typography";
+@plugin "@tailwindcss/typography";
+
+body {
+    @apply bg-white dark:bg-neutral-950;
+}

app/pages/writings/[slug].vue

@@ -8,8 +8,7 @@ const {
   refresh,
 } = await useAsyncData(`writings/${route.params.slug}/db`, () => $fetch(`/api/posts/${route.params.slug}`, { method: 'POST' }))
 
-const { locale } = useI18n()
-const { t } = useI18n({
+const { t, locale } = useI18n({
   useScope: 'local',
 })