Complete client UI i18n migration

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

packages/app/src/desktop/components/pair-device-modal.tsx

@@ -1,3 +1,5 @@
+import { useMemo } from "react";
+import { useTranslation } from "react-i18next";
 import { AdaptiveModalSheet, type SheetHeader } from "@/components/adaptive-modal-sheet";
 import { PairDeviceSection } from "@/desktop/components/pair-device-section";
 
@@ -8,12 +10,17 @@ export interface PairDeviceModalProps {
 }
 
 const SNAP_POINTS: string[] = ["82%", "94%"];
-const PAIR_DEVICE_HEADER: SheetHeader = { title: "Pair a device" };
 
 export function PairDeviceModal({ visible, onClose, testID }: PairDeviceModalProps) {
+  const { t } = useTranslation();
+  const header = useMemo<SheetHeader>(
+    () => ({ title: t("settings.integrations.pairDevices.rowTitle") }),
+    [t],
+  );
+
   return (
     <AdaptiveModalSheet
-      header={PAIR_DEVICE_HEADER}
+      header={header}
       visible={visible}
       onClose={onClose}
       snapPoints={SNAP_POINTS}