_pdf_page_geometry left rendered_w/h in PDF points (~595x842), but the app renders each PDF
page at PAGE_WIDTH=780 with proportional height and places shapes at the raw bounds. Result:
every detected region rendered shrunk (~0.76x) and shifted up-left. Set rendered_w=780 +
rendered_h=780*aspect (matches pdfLoader + pageGeometryFromImages), and scale px/point TOPLEFT
boxes into that space (was a hardcoded 0.5). Path-2 point boxes auto-correct via rendered_w/page_pt_w.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>