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/Options/ApiOptions.cs

@@ -0,0 +1,10 @@
+namespace EnvelopeGenerator.WebUI.Client.Options;
+
+public class ApiOptions
+{
+    public const string SectionName = "ApiOptions";
+
+    public string BaseUrl { get; set; } = string.Empty;
+
+    public bool UsePredefinedReports { get; set; } = false;
+}

EnvelopeGenerator.WebUI/EnvelopeGenerator.WebUI.Client/Options/PdfViewerOptions.cs

@@ -0,0 +1,71 @@
+namespace EnvelopeGenerator.WebUI.Client.Options;
+
+public class PdfViewerOptions
+{
+    public const string SectionName = "PdfViewerOptions";
+
+    /// <summary>
+    /// Base scale for thumbnail rendering (0.2 - 1.5 recommended)
+    /// Higher values = better quality but slower rendering
+    /// Default: 0.75
+    /// </summary>
+    public double ThumbnailBaseScale { get; set; } = 0.75;
+
+    /// <summary>
+    /// Enable HiDPI/Retina support for thumbnails
+    /// Default: true
+    /// </summary>
+    public bool ThumbnailEnableHiDPI { get; set; } = true;
+
+    /// <summary>
+    /// Maximum device pixel ratio multiplier for thumbnails (1.0 - 3.0)
+    /// Caps DPR to avoid excessive memory usage on 4K+ displays
+    /// Default: 2.0
+    /// </summary>
+    public double ThumbnailMaxDPR { get; set; } = 2.0;
+
+    /// <summary>
+    /// Enable HiDPI/Retina support for main PDF canvas
+    /// Default: true
+    /// </summary>
+    public bool MainCanvasEnableHiDPI { get; set; } = true;
+
+    /// <summary>
+    /// Maximum device pixel ratio multiplier for main canvas (1.0 - 3.0)
+    /// Default: 2.0
+    /// </summary>
+    public double MainCanvasMaxDPR { get; set; } = 2.0;
+
+    /// <summary>
+    /// Enable smooth zoom transition (fade effect)
+    /// Default: true
+    /// </summary>
+    public bool EnableSmoothZoom { get; set; } = true;
+
+    /// <summary>
+    /// Zoom transition duration in milliseconds (50 - 500)
+    /// Default: 150
+    /// </summary>
+    public int ZoomTransitionDuration { get; set; } = 150;
+
+    /// <summary>
+    /// Opacity during rendering (0.0 - 1.0)
+    /// Lower values = more visible fade effect
+    /// Default: 0.85
+    /// </summary>
+    public double RenderingOpacity { get; set; } = 0.85;
+
+    /// <summary>
+    /// Delay between thumbnail renders in milliseconds (10 - 200)
+    /// Higher values = less browser stress, slower initial load
+    /// Default: 50
+    /// </summary>
+    public int ThumbnailRenderDelay { get; set; } = 50;
+
+    /// <summary>
+    /// Zoom step percentage (1 - 50)
+    /// Controls how much zoom changes per click or scroll
+    /// Default: 5 (5% per step)
+    /// </summary>
+    public int ZoomStepPercentage { get; set; } = 5;
+}