- Replaced button in `Details.cshtml` with a link to a new document viewer page.
- Created `DocumentViewer.cshtml` to display PDFs using an iframe, with a back button and a link to an experimental DevExpress viewer.
- Introduced `DocumentViewerModel` in `DocumentViewer.cshtml.cs` for handling invoice ID and PDF URL.
- Updated `OnGetAsync` in `ViewPdf.cshtml.cs` to set `Content-Disposition` to inline for better PDF rendering in the browser.
