Get open issue / open PR counts for a list of GitHub repos.

Developer-UI helper for the plugin cards. Accepts a comma-separated list of owner/name repos and returns per-repo { openIssues, openPRs }. Counts are proxied from GitHub's issue-search API (one aggregate query per group of repos, cached per box), never one request per plugin -- which is what floods the device with 404s when there is no network or a repo is gone. Fail-soft: on any upstream problem it serves a stale cache if present, else an empty map (source: unavailable); the UI then hides the corner counts.