Complete client UI i18n migration

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

packages/app/src/components/sidebar-callout.tsx

@@ -2,6 +2,7 @@ import { X } from "lucide-react-native";
 import { useCallback, useMemo, type ReactNode } from "react";
 import { Pressable, Text, View, type PressableStateCallbackType } from "react-native";
 import { StyleSheet, useUnistyles } from "react-native-unistyles";
+import { useTranslation } from "react-i18next";
 
 export type SidebarCalloutActionVariant = "primary" | "secondary";
 
@@ -38,6 +39,7 @@ export function SidebarCallout({
   onDismiss,
   testID,
 }: SidebarCalloutProps) {
+  const { t } = useTranslation();
   const { theme } = useUnistyles();
   const visibleActions = (actions ?? []).slice(0, 2);
   const hasHeader = title != null || icon != null;
@@ -69,7 +71,7 @@ export function SidebarCallout({
                 hitSlop={8}
                 style={styles.dismissButton}
                 testID={testID ? `${testID}-dismiss` : undefined}
-                accessibilityLabel="Dismiss"
+                accessibilityLabel={t("sidebarCallout.dismiss")}
                 accessibilityRole="button"
               >
                 {({ hovered }) => (