Introduced `PdfViewerOptions` class to centralize PDF viewer
settings such as scaling, HiDPI support, zoom transitions,
and rendering delays. Bound these options to `appsettings.json`
for dynamic configuration.
Injected `PdfViewerOptions` into `EnvelopeViewer.razor` and
updated `OnInitializedAsync` to pass settings to JavaScript.
Replaced hardcoded values in `pdf-viewer.js` with configurable
options, improving maintainability and flexibility.
Enhanced rendering logic to respect HiDPI settings, maximum
DPR, and smooth zoom transitions. Improved thumbnail rendering
with configurable delays to optimize performance.