Complete client UI i18n migration

Adds client-side i18n support, language settings, translated UI copy, and locale parity coverage.

packages/app/package.json

@@ -73,6 +73,7 @@
     "expo-image-picker": "^17.0.8",
     "expo-keep-awake": "^15.0.7",
     "expo-linking": "~8.0.8",
+    "expo-localization": "~17.0.9",
     "expo-notifications": "^0.32.16",
     "expo-router": "~6.0.13",
     "expo-sharing": "^14.0.8",
@@ -80,12 +81,14 @@
     "expo-system-ui": "~6.0.7",
     "expo-updates": "~29.0.12",
     "fast-deep-equal": "^3.1.3",
+    "i18next": "^26.3.0",
     "lucide-react-native": "^0.546.0",
     "markdown-it": "^10.0.0",
     "mnemonic-id": "^3.2.7",
     "qrcode": "^1.5.4",
     "react": "19.1.0",
     "react-dom": "19.1.0",
+    "react-i18next": "^17.0.8",
     "react-native": "0.81.5",
     "react-native-draggable-flatlist": "^4.0.3",
     "react-native-edge-to-edge": "^1.7.0",