Enable Blazor-JS communication for PDF viewer zoom

Added `DotNetObjectReference` in `EnvelopeViewer.razor` to enable Blazor-JS communication. Updated `OnAfterRenderAsync` to pass the reference to `pdfViewer.initialize`. Introduced `[JSInvokable]` method `OnZoomChanged` to handle zoom updates from JavaScript.

Enhanced `DisposeAsync` to clean up resources, including disposing of the `.NET reference` and invoking a JavaScript `dispose` method.

In `pdf-viewer.js`, modified `initialize` to accept a `.NET reference` and added `attachWheelEvent` to handle zooming via mouse wheel with `Ctrl`/`Meta` key. Updated `dispose` to clean up event listeners and reset the `.NET reference`. Added `getScale` to retrieve the current zoom scale.

Improved resource cleanup and event handling to prevent memory leaks and ensure stability.

EnvelopeGenerator.ReceiverUI/Pages/EnvelopeViewer.razor

@@ -117,6 +117,7 @@
     int _currentPage = 1;
     int _totalPages = 0;
     int _currentZoom = 150;
+    DotNetObjectReference<EnvelopeViewer>? _dotNetRef;
 
     protected override async Task OnInitializedAsync() {
         if (string.IsNullOrWhiteSpace(EnvelopeKey)) {
@@ -147,7 +148,8 @@
             await Task.Delay(500);
             
             try {
-                var success = await JSRuntime.InvokeAsync<bool>("pdfViewer.initialize", "pdf-canvas", _pdfDataUrl);
+                _dotNetRef = DotNetObjectReference.Create(this);
+                var success = await JSRuntime.InvokeAsync<bool>("pdfViewer.initialize", "pdf-canvas", _pdfDataUrl, _dotNetRef);
                 
                 if (success) {
                     _pdfLoaded = true;
@@ -162,6 +164,13 @@
         }
     }
 
+    [JSInvokable]
+    public async Task OnZoomChanged(double scale)
+    {
+        _currentZoom = (int)(scale * 100);
+        await InvokeAsync(StateHasChanged);
+    }
+
     async Task NextPage() {
         if (await JSRuntime.InvokeAsync<bool>("pdfViewer.nextPage")) {
             _currentPage = await JSRuntime.InvokeAsync<int>("pdfViewer.getCurrentPage");
@@ -187,6 +196,13 @@
     }
 
     public async ValueTask DisposeAsync() {
-        // Cleanup if needed
+        if (_pdfLoaded) {
+            try {
+                await JSRuntime.InvokeVoidAsync("pdfViewer.dispose");
+            } catch {
+                // Ignore errors during disposal
+            }
+        }
+        _dotNetRef?.Dispose();
     }
 }