Enhance PDF viewer with annotations and WebAssembly

Added support for advanced annotation tools, including signature and stamp management, along with accessibility improvements. Introduced WebAssembly binaries (`qcms_bg.wasm`, `quickjs-eval.wasm`, `openjpeg.wasm`, `jbig2.wasm`) for enhanced performance in color management, JavaScript execution, and image decoding.

Implemented a JavaScript fallback (`openjpeg_nowasm_fallback.js`) for environments without WebAssembly support. Updated `Details.cshtml` to include a PDF viewer popup and added a new Razor Page (`ViewPdf.cshtml`) for secure PDF file access. Registered `.mjs` MIME type in `Program.cs` for PDF.js compatibility.

Enhanced localization with translations for multiple languages in `viewer.ftl` and added new icons, dialogs, and accessibility features. Updated `DXApp.sln` to include a new project for template management. These changes improve functionality, modularity, and user experience.

DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml

@@ -7,6 +7,14 @@
 <h2>📄 Rechnungsdetails</h2>
 <a href="/Invoices" class="btn btn-secondary mb-3">← Zurück zur Liste</a>
 
+@if (!string.IsNullOrEmpty(Model.Invoice?.ResultFilePath))
+{
+    <button class="btn btn-primary mb-3 ms-2"
+            onclick="openPdfViewer(@Model.Invoice.Id)">
+        📄 PDF anzeigen
+    </button>
+}
+
 @if (Model.Invoice is null)
 {
     <div class="alert alert-danger">Rechnung nicht gefunden.</div>
@@ -41,4 +49,37 @@ else
             </td>
         </tr>
     </table>
-}
+
+@(Html.DevExtreme().Popup()
+    .ID("pdf-viewer-popup")
+    .Title("PDF Viewer")
+    .Width("90%")
+    .Height("90%")
+    .ShowCloseButton(true)
+    .OnHiding("onPdfPopupHiding")
+    .ContentTemplate(new JS(@"function() {
+        return '<iframe id=""pdf-iframe"" style=""width:100%;height:100%;border:none;""></iframe>';
+    }"))
+)
+}
+
+<script>
+    function openPdfViewer(invoiceId) {
+        var pdfUrl = window.location.origin + '/Invoices/ViewPdf?id=' + invoiceId;
+        var viewerUrl = '/js/pdfjs/web/viewer.html?file=' + encodeURIComponent(pdfUrl);
+
+        var popup = $('#pdf-viewer-popup').dxPopup('instance');
+
+        // onShown sicherstellen dass iframe im DOM ist
+        popup.option('onShown', function () {
+            $('#pdf-iframe').attr('src', viewerUrl);
+        });
+
+        popup.show();
+    }
+
+    function onPdfPopupHiding() {
+        // iframe src leeren beim Schließen → verhindert dass PDF im Hintergrund weiter läuft
+        $('#pdf-iframe').attr('src', '');
+    }
+</script>

DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml

@@ -0,0 +1,2 @@
+@page
+@model DXApp.TemplateKitProject.Pages.Invoices.ViewPdfModel

DXApp.TemplateKitProject/Pages/Invoices/ViewPdf.cshtml.cs

@@ -0,0 +1,24 @@
+using DXApp.TemplateKitProject.Data;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using Microsoft.EntityFrameworkCore;
+
+namespace DXApp.TemplateKitProject.Pages.Invoices;
+
+public class ViewPdfModel(AppDbContext db) : PageModel
+{
+    public async Task<IActionResult> OnGetAsync(int id)
+    {
+        var invoice = await db.ZugferdInvoices
+            .FirstOrDefaultAsync(i => i.Id == id);
+
+        if (invoice is null || string.IsNullOrEmpty(invoice.ResultFilePath))
+            return NotFound();
+
+        if (!System.IO.File.Exists(invoice.ResultFilePath))
+            return NotFound();
+
+        var bytes = await System.IO.File.ReadAllBytesAsync(invoice.ResultFilePath);
+        return File(bytes, "application/pdf");
+    }
+}