fix: clicking search result no longer redirects to category page

When clicking a search result, showDetail navigates to the detail page.
The route.fullPath watcher then clears searchQuery, which propagates to
Header's localSearch watcher, which emits @search='', which calls
updateSearchQuery(''). This in turn called clearSearch(), which did a
router.replace() to the category page because it didn't check whether
the current route actually had a search query.

The fix: in clearSearch(), if there's no search query in the current
URL, just clear reactive state and return without navigating. This
breaks the circular flow that was overwriting the detail-page
navigation.

frontend/src/App.vue

@@ -438,7 +438,16 @@ function clearSearch(options: { preferBack?: boolean; targetPath?: string } = {}
 
   searchQuery.value = ""
 
-  if (!currentQuery && route.path === targetPath) {
+  // If there's no active search query in the URL, just clear state and don't navigate.
+  // This prevents unwanted navigation when the search is cleared reactively (e.g.
+  // route changes to a detail page, which triggers the route watcher to clear
+  // searchQuery, which flows through Header and back to updateSearchQuery).
+  if (!currentQuery) {
+    searchReturnPath.value = null
+    return
+  }
+
+  if (route.path === targetPath) {
     searchReturnPath.value = null
     return
   }
@@ -449,7 +458,6 @@ function clearSearch(options: { preferBack?: boolean; targetPath?: string } = {}
       : ""
   const canRestoreWithBack =
     options.preferBack !== false &&
-    !!currentQuery &&
     searchReturnPath.value === targetPath &&
     backPath === targetPath