fix(ui): Default the keyboardLayout to en-US if not set (#512)

The recent fix to PasteModal will silently fail a paste if the keyboardLayout hasn't been selected in the settings yet, then when you look in Settings it looks like it's set to Belgian, but it's really just blank. Set it to default to en-US in both these places so it works like it did previously.

Fixes #492

ui/src/routes/devices.$id.settings.keyboard.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useEffect } from "react";
+import { useCallback, useEffect, useMemo } from "react";
 
 import { KeyboardLedSync, useSettingsStore } from "@/hooks/stores";
 import { useJsonRpc } from "@/hooks/useJsonRpc";
@@ -20,6 +20,13 @@ export default function SettingsKeyboardRoute() {
     state => state.setKeyboardLedSync,
   );
 
+  // this ensures we always get the original en-US if it hasn't been set yet
+  const safeKeyboardLayout = useMemo(() => {
+      if (keyboardLayout && keyboardLayout.length > 0)
+        return keyboardLayout;
+      return "en-US";
+  }, [keyboardLayout]);
+
   const layoutOptions = Object.entries(layouts).map(([code, language]) => { return { value: code, label: language } })
   const ledSyncOptions = [
     { value: "auto", label: "Automatic" },
@@ -69,7 +76,7 @@ export default function SettingsKeyboardRoute() {
             size="SM"
             label=""
             fullWidth
-            value={keyboardLayout}
+            value={safeKeyboardLayout}
             onChange={onKeyboardLayoutChange}
             options={layoutOptions}
           />