Add `.crow/weekly-patch-proposals.yaml`, a single (non-matrix) job that runs
the classifier over all of `single_builds` weekly: it posts/updates a Forgejo
tracking issue with the auto-proposable registry entries via
`propose-patches.R --open-issue`, then logs the step-4 metrics via
`proposal-tracking.R`. Clones read-only; the only write is the issue.
Register the `weekly-patch-proposals` cron in the crow UI, or trigger manually
with `task=weekly-patch-proposals`.
