- platform.sh: credential lookup falls back site-level (logins/<site>.json,
  site = first segment of source name); nikkei-world/markets/tech share one
  nikkei account, single file to maintain
- platform_layer: login_sites()/login_rows() site view (coverage, probe
  source, recipe status) for the panel
- web: /logins page now site-based — save/delete/discover/test operate per
  site; discovery probes via the site's representative source