Add cv_graphic_detect.py for detecting non-text visual elements (arrows,
circles, lines, exclamation marks, icons, illustrations). Draw detected
graphics on structure overlay image and display them in the frontend
StepStructureDetection component with shape counts and individual listings.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
New pipeline step between Crop and Columns that visualizes detected
document structure: boxes (line-based + shading), page zones, and
color regions. Shows original image on the left, annotated overlay
on the right.
Backend: POST /detect-structure endpoint + /image/structure-overlay
Frontend: StepStructureDetection component with zone/box/color details
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
