feat(news-harvester): reuters login-state detection recipe

Detection-only (checkUrl reuters.com + loggedInSelector
[data-testid=AccountButton], measured on a live logged-in session;
no steps — reuters sign-in lives on account.reuters.com, manual login
in the site instance window persists in the site-shared profile)

skills/news-harvester/logins/reuters.json

+{
+  "note": "检测型配方:仅登录态检查,不含 steps(路透登录走 account.reuters.com,自动登录未实现;人工在 reuters 站点实例窗口登录一次即可,cookie 落 profile)。已登录标志:首页头部 data-testid=AccountButton(2026-10-23 登录后实测;未登录时该位置为 Sign In 入口)。",
+  "checkUrl": "https://www.reuters.com/",
+  "loggedInSelector": "[data-testid=\"AccountButton\"]"
+}