Update DevExpress packages and add PdfViewer support

Upgraded DevExpress package references in `EnvelopeGenerator.ReceiverUI.csproj` from version 25.2.3 to 25.2.7, including:
- `DevExpress.Drawing.Skia`
- `DevExpress.Blazor.Reporting.JSBasedControls`
- `DevExpress.Blazor.Reporting.Viewer`

Added a new package reference for `DevExpress.Blazor.PdfViewer` (version 25.2.7) to enable PDF viewing functionality.

Updated `_Imports.razor` to include `@using DevExpress.Blazor.PdfViewer` for PdfViewer component support.

EnvelopeGenerator.ReceiverUI/EnvelopeGenerator.ReceiverUI.csproj

@@ -32,9 +32,10 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="8.0.11" />
     <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.DevServer" Version="8.0.11" PrivateAssets="all" />
-    <PackageReference Include="DevExpress.Drawing.Skia" Version="25.2.3" />
-    <PackageReference Include="DevExpress.Blazor.Reporting.JSBasedControls" Version="25.2.3" />
-    <PackageReference Include="DevExpress.Blazor.Reporting.Viewer" Version="25.2.3" />
+    <PackageReference Include="DevExpress.Drawing.Skia" Version="25.2.7" />
+    <PackageReference Include="DevExpress.Blazor.PdfViewer" Version="25.2.7" />
+    <PackageReference Include="DevExpress.Blazor.Reporting.JSBasedControls" Version="25.2.7" />
+    <PackageReference Include="DevExpress.Blazor.Reporting.Viewer" Version="25.2.7" />
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Properties\PublishProfiles\" />

EnvelopeGenerator.ReceiverUI/_Imports.razor

@@ -6,4 +6,5 @@
 @using EnvelopeGenerator.ReceiverUI
 @using EnvelopeGenerator.ReceiverUI.Shared
 @using DevExpress.Blazor.Reporting
+@using DevExpress.Blazor.PdfViewer
 @using DevExpress.Blazor