feat(i18n): extract remaining screens into en/zh-Hans catalogs; full Simplified Chinese coverage (closes #68) (#103)

Extends the i18n infra from #97 (Settings screen only) to the rest of the
app: session chat screen, connection add/edit/list screens, sessions list
(incl. directory grouping from #96), navigation titles, notifications
category metadata, error boundary, telemetry consent modal, auth gate, and
every chat UI component (permission/question prompts, status indicator,
model/variant pickers, directory switcher/browser, reasoning block, tool
call card, session info).

- 244 new keys added to en.json/zh-Hans.json with reviewed, natural
  Simplified Chinese (not machine-garbage), keeping key sets identical.
- User content, server URLs, code snippets, log/error-detail text, and
  diagnostics-classify.ts (pure dependency-free module feeding Sentry/
  support reports) are intentionally left untranslated per scope.
- Interpolation used for counts/names (e.g. reconnect attempt, files
  count, connection name in delete confirmations); categoryMeta/
  CONNECTION_TYPES switched to labelKey indirection since they're
  module-level constants evaluated before i18next is guaranteed ready.
- Added src/lib/i18n/catalog-parity.test.ts (node --test) asserting
  en.json/zh-Hans.json expose identical key sets and no empty values,
  to catch future locale drift.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/(tabs)/_layout.tsx

@@ -1,10 +1,12 @@
 import { Tabs } from "expo-router"
 import { useColorScheme } from "react-native"
 import { Ionicons } from "@expo/vector-icons"
+import { useTranslation } from "react-i18next"
 
 export default function TabLayout() {
   const colorScheme = useColorScheme()
   const isDark = colorScheme === "dark"
+  const { t } = useTranslation()
 
   return (
     <Tabs
@@ -24,21 +26,21 @@ export default function TabLayout() {
       <Tabs.Screen
         name="index"
         options={{
-          title: "Sessions",
+          title: t("nav.sessionsTab"),
           tabBarIcon: ({ color, size }) => <Ionicons name="chatbubbles-outline" size={size} color={color} />,
         }}
       />
       <Tabs.Screen
         name="connections"
         options={{
-          title: "Connections",
+          title: t("nav.connectionsTab"),
           tabBarIcon: ({ color, size }) => <Ionicons name="server-outline" size={size} color={color} />,
         }}
       />
       <Tabs.Screen
         name="settings"
         options={{
-          title: "Settings",
+          title: t("nav.settingsTab"),
           tabBarIcon: ({ color, size }) => <Ionicons name="settings-outline" size={size} color={color} />,
         }}
       />