fix: rework setup to improve SSR compatibility

plugins/setup-font-size.ts

@@ -0,0 +1,25 @@
+import type { FontSize } from '~/types'
+import { InjectionKeyFontSize } from '~/constants/symbols'
+import { COOKIE_KEY_FONT_SIZE } from '~/constants'
+import { fontSizeMap } from '~/constants/options'
+
+export default defineNuxtPlugin((nuxt) => {
+  const DEFAULT = 'md'
+  const cookieFontSize = useCookie<FontSize>(COOKIE_KEY_FONT_SIZE, { default: () => DEFAULT })
+  nuxt.vueApp.provide(InjectionKeyFontSize, cookieFontSize)
+
+  if (!process.server) {
+    watchEffect(() => {
+      document.documentElement.style.setProperty('--font-size', fontSizeMap[cookieFontSize.value || DEFAULT])
+    })
+  }
+  else {
+    useHead({
+      style: [
+        {
+          innerHTML: `:root { --font-size: ${fontSizeMap[cookieFontSize.value || DEFAULT]}; }`,
+        },
+      ],
+    })
+  }
+})