Add Russian i18n with DB translations, locale API, and curator review UI.

UI chrome via react-i18next, catalog text in entity_translations with ru.wikipedia seeding, locale-aware search, and Translations page for publish workflow.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/package.json

@@ -12,8 +12,10 @@
   "dependencies": {
     "@react-three/drei": "^10.7.7",
     "@react-three/fiber": "^9.6.1",
+    "i18next": "^26.3.6",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
+    "react-i18next": "^17.0.9",
     "react-router-dom": "^7.18.0",
     "three": "^0.184.0"
   },