The OCIO grading primaries expose contrast/offset/exposure as Vec4 inputs
(master + RGB); build_control had no Vec4 arm, so the inspector rendered an
empty read-only row instead of controls. Add a four-spin arm bounded by the
per-component min/max and stepped by the node's base.
Float inputs that only declare base (pivot 0.18, clampBlack/White) fell
through to the wide +/-10000 default and a single drag could hurl the value
thousands of units away; anchor the slider on value +/-100*base instead,
matching the C++ RationalSlider step semantics.
Mike-Solar
415262a7b2