QCAINotes 8

This update introduces a new subscription experience and PDF annotation support, along with improvements to the core writing workflow: - Free users can create 1 notebook; Pro unlocks unlimited notebooks. - Added PDF import and management. Free users can import 1 PDF, while Pro supports unlimited PDF imports. - Added support for handwriting, annotating, and erasing directly on PDFs. - PDF annotations are automatically saved and can be edited again after reopening. - Improved two-finger PDF zooming for smoother, more natural positioning. - Updated subscription plan display with weekly, monthly, and yearly options. - Fixed paywall price and “Free” text display in English environments. - Improved PDF file display, opening, and deletion in the library. - Refined Chinese and English interface text across the app.