Refactor ReportViewer for reusability and dynamic updates

Refactored `ReportViewer.razor` to improve maintainability and
ensure dynamic updates to the `DxReportViewer` component.

- Added `@key` attribute bound to `ViewerKey` to trigger re-renders.
- Introduced `CreateReportInstance` and `CreateSignedReportInstance`
  helper methods to encapsulate report creation logic.
- Updated `OnInitializedAsync`, `ClearSignatureAsync`, and
  `ApplySignatureAsync` to use the new helper methods.
- Incremented `ViewerKey` in relevant methods to ensure proper
  re-rendering of the `DxReportViewer` component.
- Replaced `ApplySignatureToReport` with `CreateSignedReportInstance`.

These changes improve code modularity, readability, and ensure
the UI reflects the latest state of the report.

EnvelopeGenerator.ReceiverUI/Pages/ReportViewer.razor

@@ -29,7 +29,7 @@
 </div>
 
 @if(Report is not null) {
-    <DxReportViewer @ref="reportViewer" Report="Report" RootCssClasses="w-100 h-100" />
+    <DxReportViewer @key="ViewerKey" @ref="reportViewer" Report="Report" RootCssClasses="w-100 h-100" />
 }
 
 @code {
@@ -37,11 +37,10 @@
     XtraReport? Report;
     bool SignatureApplied;
     string? SignatureValidationMessage;
+    int ViewerKey;
 
     protected override async Task OnInitializedAsync() {
-        Report = ReportStorage.TryGetReport("LargeDatasetReport", out var savedReport)
-            ? savedReport
-            : PredefinedReports.ReportsFactory.GetReport("LargeDatasetReport");
+        Report = CreateReportInstance();
 
         await Task.CompletedTask;
     }
@@ -55,12 +54,8 @@
         await JSRuntime.InvokeVoidAsync("receiverSignature.clear", "receiver-signature-pad");
         SignatureApplied = false;
         SignatureValidationMessage = null;
-        Report = ReportStorage.TryGetReport("LargeDatasetReport", out var savedReport)
-            ? savedReport
-            : PredefinedReports.ReportsFactory.GetReport("LargeDatasetReport");
-
-        if(reportViewer is not null)
-            await reportViewer.OpenReportAsync(Report);
+        Report = CreateReportInstance();
+        ViewerKey++;
     }
 
     async Task ApplySignatureAsync() {
@@ -73,11 +68,9 @@
         }
 
         SignatureValidationMessage = null;
-        ApplySignatureToReport(signatureDataUrl);
+        Report = CreateSignedReportInstance(signatureDataUrl);
         SignatureApplied = true;
-
-        if(reportViewer is not null)
-            await reportViewer.OpenReportAsync(Report);
+        ViewerKey++;
     }
 
     async Task ExportSignedPdfAsync() {
@@ -89,6 +82,18 @@
         await reportViewer.ExportToAsync(ExportFormat.Pdf);
     }
 
+    XtraReport CreateReportInstance() {
+        return ReportStorage.TryGetReport("LargeDatasetReport", out var savedReport)
+            ? savedReport
+            : PredefinedReports.ReportsFactory.GetReport("LargeDatasetReport");
+    }
+
+    XtraReport CreateSignedReportInstance(string signatureDataUrl) {
+        var report = CreateReportInstance();
+        AddSignature(report, signatureDataUrl);
+        return report;
+    }
+
     void ApplySignatureToReport(string signatureDataUrl) {
         Report ??= ReportStorage.TryGetReport("LargeDatasetReport", out var savedReport)
             ? savedReport