Converts an Anchor[] into a PageBand — no need to touch core/engine.ts at all, since it just
composes a plain PageBand (assign it to RenderEngineOptions.pageHeader = top, pageFooter =
bottom); the same align used twice in one band → throws at creation time (fail-fast, same as registerBlockType/ReportRegistry)
Converts an Anchor[] into a PageBand — no need to touch core/engine.ts at all, since it just composes a plain PageBand (assign it to RenderEngineOptions.pageHeader = top, pageFooter = bottom); the same align used twice in one band → throws at creation time (fail-fast, same as registerBlockType/ReportRegistry)