Completes env-promotion #5. The promote-from endpoint (admin, tested) and the
parent->self chain UI already shipped; the endpoint is direction-agnostic, so
this is frontend-only:
- self->child promotion: each eligible child (image source, non-preview) in
the stage chain gets a "Promote to this" button that pushes this workload's
running version to that child.
- both directions route through a ConfirmDialog (promote copies the source's
running tag onto the target AND deploys it) with a success toast.
- i18n apps.detail.chain* in en + ru (parity 1810/1810).
alexei.dolgolyov
8a5f69af87