Added bootstrap-pdfjs-preload and uikit-pdfjs-preload layouts with the full local PDF.js viewer, loading progress, height and background settings, and a download link.
Addition
PDF.js build selection and dependency checks
Added a modern/legacy switch, WT PDF.js installation and state checks, and help and validation for user JSON configuration files.
Fixed
Viewer readiness and loader styling
The preloader handles a text layer disabled in JSON. Loading and page preparation messages are centred using Bootstrap and UIkit classes in the corresponding layouts.