feat(aisummary): Return null when AI summary retrieval fails to prevent exposing issues to users

lib/plugins/aiSummary.js

@@ -27,6 +27,6 @@ export async function getAiSummary(aiSummaryAPI, aiSummaryKey, truncatedText) {
     }
   } catch (error) {
     console.error('ChucklePostAI：请求失败', error)
-    return '获取文章摘要失败，请稍后再试。'
+    return null
   }
 }