226e7b2 un-flipped the canvas but left destinationRect anchored at
pageRect.minY — the page's BOTTOM edge in bottom-up space — so
sub-page targets printed at the foot of the sheet and oversize
targets clipped their top rows. Anchor at pageRect.maxY - height,
restoring the spec'd top-left anchor (docs/14 §6, D9).
Adds the missing regression coverage: the geometry test now asserts
the top anchor with a sub-page raster, and the PDF harness gains a
banded (red-over-blue) fixture that fails on either a mirrored draw
or a bottom anchor — solid fills could catch neither.