* ci: build matrix legs without include so selected services actually build Matrix include entries whose service is not in the selected list are not merged into a combination — GitHub creates a new combination from them. In the old workflow that silently built all seven images on every push; after the per-platform split those stray combinations had no runner, so the whole build job was rejected and merge ran with no digests. Expand service × platform (with context, dockerfile, runner) in the prepare job with jq and feed it to the build job as an explicit include list. Also drop the empty-string entry produced when no service matched. * ci: speedup ---------