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/i18n.ts

@@ -0,0 +1,15 @@
+import { createI18n } from 'vue-i18n'
+import en from './locales/en.json'
+
+export type MessageSchema = typeof en
+
+const i18n = createI18n<[MessageSchema], 'en'>({
+  legacy: false,
+  locale: 'en',
+  fallbackLocale: 'en',
+  messages: {
+    en,
+  },
+})
+
+export default i18n