Jumoo Releases: engineering activity on the activity page

Repo: Jumoo/releases

Added an "At a glance" summary and an "Engineering activity" section (12-month issues/PRs/commits chart + per-package table) to the activity page
New scripts/seed-engagement.mjs: one-off historical backfill of issues/PRs/commits per package per month, paginating full GitHub history
New scripts/fetch-engagement.mjs: incremental refresh wired into the release workflow, recomputes a rolling 13-month window and replaces it wholesale each run to avoid double-counting reopened/updated issues
Renamed the existing table to "Commit activity" and made both sections collapsible, matching the stats page