weekly-rebuild-reindex depends on weekly-rebuild-missing and shares its
gate, so triggering it manually also starts hours of package rebuilds.
That is the wrong tool when only the index needs regenerating: after a
bincraft release that changes how the index is written, the objects in
the bucket are already correct and only PACKAGES* is stale.
This workflow does the index half alone. It installs the latest bincraft
release, republishes the generic and per-R-minor indexes for each slot,
and purges the edge. No package is built.
