In effect dialogs (like Color Halftone), length fields with defined bounds
(e.g. Max Radius 4..127 pt) were previously checked only after num_field
returned, leaving the field's temporary buffer holding the un-clamped string
(e.g. '0.5 px'). Subsequently entering invalid text caused the field to
fall back to that sub-minimum buffer.
- Added num_field_within to pass effect parameter bounds directly to unit_field.
- When committed, clamp the parsed value within bounds and update the field
buffer to the formatted clamped value so the UI reflects what is applied.
- When invalid text is committed, clear the invalid buffer and trigger a
one-frame border highlight so invalid input is rejected visibly.