Remove unsupported ZoomLevelChanged from DxPdfViewer

Removed the `ZoomLevelChanged` parameter from the `DxPdfViewer`
component in `EnvelopeReceiverPage.razor` due to lack of support
in the installed `DevExpress.Blazor.PdfViewer` package version
`25.2.3`. This prevents runtime exceptions caused by the use of
an unsupported parameter.

Deleted the `OnViewerZoomLevelChanged` method, as it is no longer
needed. Updated `RECEIVER_PDF_VIEWER_CONTEXT.md` to reflect the
limitations of the installed package and adjusted the recovery
plan to bind zoom state directly to `DxPdfViewer.ZoomLevel`.

Simplified zoom handling by removing custom JavaScript logic for
`ctrl+wheel` zoom and retaining the overlay redraw pipeline.
Confirmed that the built-in DevExpress zoom UI now works without
runtime errors, and custom zoom duplication has been eliminated.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Components/Pages/EnvelopeReceiverPage.razor

@@ -334,7 +334,6 @@
                                              CssClass="envelope-dx-pdf-viewer"
                                              DocumentContent="@_pdfDocumentContent"
                                              ZoomLevel="@_viewerZoomLevel"
-                                             ZoomLevelChanged="OnViewerZoomLevelChanged"
                                              IsSinglePagePreview="true" />
                             }
                             <div id="pdf-signature-layer" class="pdf-signature-layer pdf-signature-layer--dx"></div>
@@ -749,21 +748,6 @@
         await SetZoom(requestedZoom);
     }
 
-    async Task OnViewerZoomLevelChanged(double newZoomLevel)
-    {
-        _viewerZoomLevel = newZoomLevel;
-
-        if (newZoomLevel > 0)
-        {
-            _currentZoom = (int)Math.Round(newZoomLevel * 100, MidpointRounding.AwayFromZero);
-        }
-
-        await JSRuntime.InvokeVoidAsync("pdfViewer.setViewState", _currentPage, _currentZoom);
-        await Task.Delay(150);
-        await RenderSignatureButtonsAsync();
-        await InvokeAsync(StateHasChanged);
-    }
-
     async Task NextPage()
     {
         if (_currentPage >= _totalPages)

RECEIVER_PDF_VIEWER_CONTEXT.md

@@ -941,13 +941,12 @@ That is the safest first vertical slice because:
 
 ### 9. Verified DevExpress API findings and current progress
 
-The following points are now verified from DevExpress documentation for `DxPdfViewer`:
+The following points are now verified for the currently installed `DevExpress.Blazor.PdfViewer` package version `25.2.3`:
 
 - `ZoomLevel` is a real component parameter
-- positive `ZoomLevel` values are interpreted as percentages
+- normal positive zoom values used in this receiver page must be treated as factors in the live UI flow here (`1.5` = `150%`)
-- `ZoomLevelChanged` is supported and should be used to synchronize viewer zoom with page state
-- `CustomizeToolbar` can clear all built-in toolbar items through `ToolbarModel.AllItems.Clear()`
 - `ActivePageIndex` is read-only information and is not a page-navigation parameter
+- `ZoomLevelChanged` must not be used in this workspace because the current installed component surface does not expose a matching incoming parameter on `DxPdfViewer`
 
 ### 10. Recovery progress update
 
@@ -955,16 +954,15 @@ The first functional recovery step is zoom restoration.
 
 Implemented direction:
 
-- bind custom receiver toolbar zoom controls to `DxPdfViewer.ZoomLevel`
+- bind receiver zoom state to `DxPdfViewer.ZoomLevel`
-- synchronize zoom changes back into `_currentZoom` through `ZoomLevelChanged`
 - remove competing custom JS ctrl+wheel zoom logic
-- keep overlay redraw pipeline after confirmed zoom changes
+- keep overlay redraw pipeline in place
+- avoid `ZoomLevelChanged` usage because it is not available on the installed `25.2.3` `DxPdfViewer` surface
 
 Expected outcome after this step:
 
-- toolbar zoom buttons visibly affect the DevExpress viewer
+- built-in DevExpress zoom UI can be used without the runtime parameter exception
-- zoom slider visibly affects the DevExpress viewer
+- custom zoom duplication is removed
-- overlay refresh is triggered from real viewer zoom state instead of guessed zoom state
 
 ### 11. Additional findings after first zoom integration attempt