refactor(i18n): isolate Vue I18n instances per request for SSR

Replace global I18n singleton with a factory function
Inject request-specific I18n instances into Nuxt app and SEO metadata
Prevent cross-request locale state pollution during server-side rendering

frontend/plugins/01-i18n.ts

@@ -1,5 +1,15 @@
-import { i18n } from '../src/i18n';
+import { createPokopiaI18n, setActiveI18n } from '../src/i18n';
 
 export default defineNuxtPlugin((nuxtApp) => {
+  const i18n = createPokopiaI18n();
+  if (import.meta.client) {
+    setActiveI18n(i18n);
+  }
+
   nuxtApp.vueApp.use(i18n);
+  return {
+    provide: {
+      pokopiaI18n: i18n
+    }
+  };
 });

frontend/plugins/02-seo.ts

@@ -1,11 +1,13 @@
 import { computed, ref } from 'vue';
 import { onLocaleChange } from '../src/i18n';
-import { applyRouteSeo, onSeoChange, resolveRouteSeo, type ResolvedSeoConfig } from '../src/seo';
+import { applyRouteSeo, onSeoChange, resolveRouteSeo, setSeoTranslator, type ResolvedSeoConfig } from '../src/seo';
 
 export default defineNuxtPlugin(() => {
   const router = useRouter();
+  const nuxtApp = useNuxtApp();
+  const t = (nuxtApp.$pokopiaI18n as { global: { t: (key: string, values?: Record<string, string | number>) => string } }).global.t;
   const dynamicSeo = ref<ResolvedSeoConfig | null>(null);
-  const activeSeo = computed(() => dynamicSeo.value ?? resolveRouteSeo(router.currentRoute.value));
+  const activeSeo = computed(() => dynamicSeo.value ?? resolveRouteSeo(router.currentRoute.value, t));
 
   useHead(() => ({
     title: activeSeo.value.title,
@@ -42,6 +44,7 @@ export default defineNuxtPlugin(() => {
     return;
   }
 
+  setSeoTranslator(t);
   onSeoChange((seo) => {
     dynamicSeo.value = seo;
   });