fix: SearXNG 引擎优先级调整 — Bing 置顶，百度垫底

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/ai-core/internal/tools/web_search.go

@@ -97,7 +97,7 @@ func (t *WebSearchTool) Execute(ctx context.Context, arguments map[string]interf
 }
 
 func (t *WebSearchTool) searchViaSearXNG(ctx context.Context, query string) (*ToolResult, error) {
-	apiURL := fmt.Sprintf("%s/search?format=json&engines=baidu,sogou,360search,bing&q=%s",
+	apiURL := fmt.Sprintf("%s/search?format=json&engines=bing,sogou,360search,baidu&q=%s",
 		t.searxngURL, url.QueryEscape(query))
 
 	req, err := http.NewRequestWithContext(ctx, "GET", apiURL, nil)