fix(i18n): preserve locale toggle query state

Author: sonwr

frontend/src/components/LocaleToggle.tsx

@@ -1,27 +1,28 @@
 "use client";
 
-import { useParams, usePathname } from "next/navigation";
+import { useMemo } from "react";
+import { useParams, usePathname, useSearchParams } from "next/navigation";
 
 export function LocaleToggle() {
   const { locale } = useParams<{ locale: string }>();
   const pathname = usePathname();
+  const searchParams = useSearchParams();
 
   const otherLocale = locale === "ko" ? "en" : "ko";
   const toggleLabel = locale === "ko" ? "Switch to English" : "한국어로 전환";
   const normalizedPath = pathname.startsWith(`/${locale}`)
     ? pathname
     : `/${locale}${pathname}`;
   const safePath = normalizedPath.replace(new RegExp(`^/${locale}(?=/|$)`), `/${otherLocale}`);
-
-  // Replace /{locale} prefix in pathname
-  const newPath = safePath;
+  const queryString = useMemo(() => searchParams.toString(), [searchParams]);
+  const newPath = queryString ? `${safePath}?${queryString}` : safePath;
 
   return (
     <a
       href={newPath}
       className="flex items-center gap-1.5 px-3 py-1.5 border border-hud-border hover:border-accent bg-void-light/80 rounded font-mono text-sm text-hud-muted hover:text-accent transition-colors"
       title={toggleLabel}
-      aria-label={toggleLabel}
+      aria-label={`${toggleLabel}. Keep current filters and view state.`}
     >
       <span className={locale === "ko" ? "text-hud-muted" : "text-accent font-semibold"}>EN</span>
       <span className="text-hud-label">/</span>