Display a set of mutually exclusive choices as groups of a radio image
and text label. Each image and label uses immediate input and routes
every Selected notification to the containing Radio's Active setter with
its own index. Clicking the label or image therefore selects the same
choice. The class owns the constructed child groups and an array of
child pointers.
Construction requires Entries. Each Text child copies its label; Radio
does not retain the input array. Initial Active defaults to zero and an
out-of-range value is replaced by zero. Child construction and
notification registration do not have comprehensive individual failure
checks. A NULL Entries argument follows an early disposal/failure path
before superclass construction; provide a valid nonempty array.
Setup delegates first, returns FALSE on superclass failure, then sets
horizontal and vertical Group spacing from the radio-button preferences
and returns TRUE. Dispose frees the pointer array and delegates child
disposal to Group. Serialize setters and child callbacks with disposal;
no additional lifetime or locking mechanism is provided.