feat: add vue-i18n infrastructure and externalize all UI strings (A11Y-03)

Set up vue-i18n with English locale file containing 500+ keys organized
by view namespace. All 15 views converted to use t() calls instead of
hardcoded strings. Infrastructure ready for community translations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/src/main.ts

@@ -3,11 +3,13 @@ import { createPinia } from 'pinia'
 import './style.css'
 import App from './App.vue'
 import router from './router'
+import i18n from './i18n'
 
 const app = createApp(App)
 const pinia = createPinia()
 
 app.use(pinia)
 app.use(router)
+app.use(i18n)
 
 app.mount('#app')