Coordinated upgrade of core rc.10 -> 2.0.4 and promotion of
admin2/api/flex-objects to GPM management (option B). Documents the
dependency-forced atomicity, the three plugin-management categories,
git-sync handling (disable-during-upgrade, remote-only), and the
local -> test -> prod(documented-only) rollout.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
