fix: web_search结果注入批量抓取引导，AGENT.md加强链式调用描述，避免AI只抓一条

src/renderer/services/agent-engine.ts

@@ -222,7 +222,13 @@ function formatToolResultForModel(toolName: string, result: ToolResult): string
       const top = raw.slice(0, 5).map((r, i) =>
         `[${i + 1}] ${r.title}\n    URL: ${r.url}\n    ${r.snippet}`
       ).join('\n\n');
-      return JSON.stringify({ success: true, query: result.query, total: result.total, results: top });
+      return JSON.stringify({
+        success: true,
+        query: result.query,
+        total: result.total,
+        results: top,
+        _next: `以上是搜索结果摘要。请对前 ${Math.min(5, raw.length)} 条中与用户问题相关的条目，逐一调用 web_fetch 获取详细内容后再综合回答。不要只抓取一条！每条抓取都是独立的 web_fetch 调用。`
+      });
     }
 
     case 'web_fetch': {