Don’t recompile without transform/dependency change

Because any change to a file updates its metadata, and metadata is
a dependency of the main transform, changing any file used to require
recompiling all of them. This is needlessly expensive: Files should
only be recompiled for changes to files they actually depend on. (Of
course, files might have an undeclared dependency, but relying on this
is at user’s own risk.)

This commit changes compiled files to depend only on the transform
catalog, not the transform itself, and only the metadata of files they
depend on (which presumably will always be updated alongside the
files). The main transform itself is now a make·file prerequisite,
mirroring the main parser, to ensure it is always current even tho no
compilation properly depends on it anymore.