Add signature workflow models, services, and configurations

Introduced new models (`SignatureDto`, `SignatureCaptureDto`, `EnvelopeReceiverDto`) to support a signature-based workflow. Added services for handling API interactions (`SignatureService`, `AuthService`, `DocumentService`, `EnvelopeReceiverService`, `SignatureCacheService`).

Enhanced configuration with `ApiOptions` and `PdfViewerOptions`. Integrated DevExpress features with custom data connection providers, in-memory report storage, and font loading utilities.

Marked `AnnotationDto` and `AnnotationService` as `[Obsolete]` in favor of newer implementations. Added detailed documentation for coordinate systems, unit conversions, and usage scenarios.

EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI.Client/Services/AppVersionService.cs

@@ -0,0 +1,26 @@
+namespace EnvelopeGenerator.WebUI.Client.Services;
+
+/// <summary>
+/// Provides application version for cache busting static assets.
+/// Version is automatically incremented on each build via AssemblyVersion.
+/// </summary>
+public class AppVersionService
+{
+    /// <summary>
+    /// Current application version (e.g., "1.0.0.0")
+    /// </summary>
+    public string Version { get; }
+
+    public AppVersionService()
+    {
+        // Get version from assembly metadata
+        Version = typeof(AppVersionService).Assembly.GetName().Version?.ToString() ?? "1.0.0.0";
+    }
+
+    /// <summary>
+    /// Generates versioned URL for static assets (cache busting)
+    /// </summary>
+    /// <param name="path">Asset path (e.g., "css/envelope-viewer.css")</param>
+    /// <returns>Versioned URL (e.g., "css/envelope-viewer.css?v=1.0.0.0")</returns>
+    public string GetVersionedUrl(string path) => $"{path}?v={Version}";
+}