backstage release v2.16.0

Added

• GPU node pools show every step after Remove — the row reads removing… with the teardown until the pool is gone; a refused Remove renders cluster-manager’s structured refused block (nodes, models, hint) with Check again, Remove anyway a second choice; a partial Remove is continued in #2423 by @teemow

Full Changelog: https://github.com/giantswarm/backstage/compare/v2.15.0...v2.16.0