Add signature caching and logging to EnvelopeViewer

Introduced `SignatureCacheService` and `ILogger<EnvelopeViewer>` to enable caching and logging functionality. Added logic to load cached signatures when available, bypassing the signature popup. Implemented asynchronous, fire-and-forget caching of captured signatures, with error handling to ignore cache failures. Updated signature handling to integrate with the caching mechanism, improving user experience and performance.

EnvelopeGenerator.ReceiverUI/Pages/EnvelopeViewer.razor

@@ -12,9 +12,11 @@
 @inject IOptions<PdfViewerOptions> PdfViewerOptions
 @inject IJSRuntime JSRuntime
 @inject SignatureService SignatureService
+@inject SignatureCacheService SignatureCacheService
 @inject EnvelopeGenerator.ReceiverUI.Services.AuthService AuthService
 @inject EnvelopeGenerator.ReceiverUI.Services.EnvelopeReceiverService EnvelopeReceiverService
 @inject AppVersionService AppVersion
+@inject ILogger<EnvelopeViewer> logger
 @implements IAsyncDisposable
 
 <link href="_content/DevExpress.Blazor.Themes/blazing-berry.bs5.min.css" rel="stylesheet" />
@@ -563,10 +565,34 @@ const int MaxThumbnailWidth = 400;
 
             await JSRuntime.InvokeVoidAsync("console.log", "Loaded signatures:", _signatures);
 
-            // Open signature popup on page load
+            // Try to load cached signature first
-            _activeSignatureTab = SignatureTabDraw;
+            try
-            _signaturePopupVisible = true;
+            {
-            _popupValidationMessage = null;
+                var cachedSignature = await SignatureCacheService.GetSignatureAsync(EnvelopeKey);
+                if (cachedSignature is not null)
+                {
+                    _capturedSignature = cachedSignature;
+                    _signerFullName = cachedSignature.FullName;
+                    _signerPosition = cachedSignature.Position;
+                    _signaturePlace = cachedSignature.Place;
+                    _signaturePopupVisible = false;
+                    
+                    logger.LogInformation("Cached signature loaded for envelope {EnvelopeKey}", EnvelopeKey);
+                }
+                else
+                {
+                    _activeSignatureTab = SignatureTabDraw;
+                    _signaturePopupVisible = true;
+                    _popupValidationMessage = null;
+                }
+            }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Failed to load cached signature, showing popup");
+                _activeSignatureTab = SignatureTabDraw;
+                _signaturePopupVisible = true;
+                _popupValidationMessage = null;
+            }
 
         } catch (Exception ex) {
             _errorMessage = $"Fehler: {ex.Message}";
@@ -881,6 +907,22 @@ const int MaxThumbnailWidth = 400;
         };
         _signaturePopupVisible = false;
         
+        // Save to cache (fire-and-forget, ignore errors)
+        if (!string.IsNullOrWhiteSpace(EnvelopeKey))
+        {
+            _ = Task.Run(async () =>
+            {
+                try
+                {
+                    await SignatureCacheService.SaveSignatureAsync(EnvelopeKey, _capturedSignature);
+                }
+                catch
+                {
+                    // Ignore cache errors
+                }
+            });
+        }
+        
         await InvokeAsync(StateHasChanged);
         Console.WriteLine($"Signature saved: {_signerFullName}, {_signaturePlace}");
     }