* fix(layout): resolve design token variables before passing to yoga-layout
applyPadding() and applyAutoLayout() passed variable references like
$--spacing-lg directly to yoga-layout's setPadding()/setGap() which
expects numeric values, causing a crash.
Now resolves variable references via ctx.resolveNumber() before
assignment, following the same pattern already used by parseSize()
and applyCornerRadius() in the same file.
Fixes open-pencil/open-pencil#201
* test(layout): add regression tests for variable padding/gap resolution (#201)
