Editing an environment value leaves project overrides alone, which is the
right semantics but was invisible: a project kept its own value and nothing
said so. At environment scope the layers icon now counts the projects that
override the key, and the chain lists them per environment with their
values. A project name jumps the breadcrumb to that project; Reset all
drops that key from those projects' entries so they follow the environment
again. No confirmation: the list is the confirmation and the change is one
click to redo.