Layer 0 registry of available theme names.
The Editor's Theme module registers builtin and user themes here at boot time. Config.Options and Config.Completion query this list for validation and tab-completion without importing from MingaEditor.*.
Summary
Functions
Returns the sorted list of available theme name atoms.
Registers the full list of available theme names (builtins + user).
Seeds the registry with builtin themes. Called at application start.