Adds (or replaces) an entry in the internal atlas registry.
Arguments
- id
Canonical atlas id (character scalar).
- label
Human-readable label.
- family
Atlas family (e.g. `"schaefer"`, `"glasser"`).
- loader
Name of the loader function (character scalar); resolved via [getExportedValue()] / [get()] at dispatch time.
- default_space
Default template space the loader returns when given no explicit `outspace` argument.
- representation
One of `"volume"`, `"surface"`, or `"derived"`.
- aliases
Optional character vector of accepted aliases.
- description
Optional free-text description.