Pure geometry, no I/O: DIN A6-A2 incl. A3+ (329x483), photo-paper cuts,
US Letter/Legal, biometric and small photo formats, plus a forgiving free
size parser (12x15 cm, 35x45mm, 5, 4:3/15). Packing: exact grid for uniform
sizes, MaxRects with one fixed orientation per format for mixed sets, so
small prints fill the space next to a large one. Crop marks as line segments
(corner marks outside the trim box; continuous guides that never cross a
motif). Covered by tests/printlayout.test.ts.
