fix(api): surface LLM network errors for WeCom AI replies

Co-authored-by: Cursor <cursoragent@cursor.com>

server/dukang-api/src/integrations/llm/llm-chat.client.ts

@@ -50,6 +50,14 @@ export class LlmChatClient {
         Authorization: `Bearer ${params.apiKey}`,
       },
       body: JSON.stringify(body),
+    }).catch((err: unknown) => {
+      const cause =
+        err && typeof err === 'object' && 'cause' in err
+          ? (err as { cause?: { code?: string; message?: string } }).cause
+          : undefined;
+      const detail = cause?.code || cause?.message || (err instanceof Error ? err.message : String(err));
+      this.logger.warn(`llm chat network error ${url}: ${detail}`);
+      throw new Error(`无法连接语言模型服务（${detail}）。请检查 Base URL 是否可从服务器访问，或更换可达的模型网关`);
     });
 
     const text = await res.text();