PERF.27 Scale: MarkupCraft reads the whole PDF twice and keeps the whole PDF per autosave; OBJ import refuses at 64 MB where the same model as GLB imports fine

Two small ones from the scale track. (1) pdf.js is healthy (2,000 sheets open in 0.6 s, lazy), but markupcraft.js:1158 and :1206 read the file twice, the second time only to count pages; and the autosave stores the whole PDF Blob each time: count pages from the first open, keep a file handle or the original bytes once. (2) ModelCraft io/obj.js:32 refuses OBJ above 64 MB (about 1.7 M faces) with an honest message while the same model as a 400 MB GLB imports in 17 s; lift the cap with the byte scanner and typed arrays from the streaming readers row.