feat(project): sweep the whole org onto the board from a public runner

[ExtraToast]

What

Adds org-project-sweep.yml — a scheduled workflow that boards every open issue and PR across the organization, running from this public repo.

Companion to JorisJonkers-dev/github-workflows#124, which adds the scope: org input this calls.

Why it lives here

Actions minutes are billed to the caller, never to the repo holding the reusable workflow. The per-repo uses: shims already point at github-workflows and that saves nothing — a private repo firing the event pays for the run.

Standard runners are free in public repositories. This repo is public, so every run of this sweep costs nothing. That is also why the cron can be */15 — there is no minute budget to ration, only GitHub's own scheduling latency.

Boarding across the private repos currently costs ~516 billable minutes/month for a job that averages 7 seconds and reads no repository content.

Second reason this is worth having

When GitHub stops creating runs from webhook events — which has happened in this estate, stranding 24 issues at once — the event-driven path silently stops boarding anything, and there is no signal that it has. A sweep keeps working, because it isn't waiting on a webhook.

Notes

• concurrency with cancel-in-progress: false so a slow sweep doesn't stack behind the next tick
• The existing event-driven add-to-project-caller.yml in this repo is left alone — it's free here and boards instantly
• Scheduled workflows are disabled after 60 days of repo inactivity; worth knowing if this repo ever goes quiet

Merge order

Merge JorisJonkers-dev/github-workflows#124 first — this calls @main and will fail until scope: org exists there.

Refs #33