feat: add session grouping, improve chart sorting, and optimize crop loading

Add stacked chart with topic ratios and subject filtering

feat: refactor revision notes to store JSON instead of rasterized images

feat: add auto-save functionality to question entry form

fix: create question row if missing when saving classification

feat: redesign revision notes system with separate handwritten canvas

new features

fix: consolidate pending fixes for PDF manager UI, dashboard filtering, and SQL syntax

fix: add missing uuid import in pdf_ops.py to resolve 500 error in merge and resize operations

fix: resolve NameError in processing.py and restore missing question routes

fix: correct import of create_pdf_from_full_images in pdf_ops.py

refactor: modularize routes.py into dedicated package