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/Models/SignatureDto.cs

@@ -0,0 +1,101 @@
+using EnvelopeGenerator.WebUI.Client.Models.Constants;
+
+namespace EnvelopeGenerator.WebUI.Client.Models;
+
+/// <summary>
+/// Represents a signature position on a PDF page.
+/// Coordinates stored in INCHES (GdPicture14 native unit).
+/// Origin: Top-left corner, X increases right, Y increases down.
+/// </summary>
+public class SignatureDto
+{
+    /// <summary>Unique identifier.</summary>
+    public int Id { get; init; }
+
+    private double _x;
+    private double _y;
+
+    /// <summary>Horizontal position in INCHES from left edge.</summary>
+    public double X 
+    { 
+        get => _x * Factor;
+        init => _x = value; 
+    }
+
+    /// <summary>Vertical position in INCHES from top edge.</summary>
+    public double Y 
+    { 
+        get => _y * Factor;
+        init => _y = value; 
+    }
+
+    /// <summary>1-based page number.</summary>
+    public int Page { get; init; }
+
+    /// <summary>Sender application type that created this signature.</summary>
+    public SenderAppType SenderAppType { get; init; }
+
+    private UnitOfLength _unitOfLength;
+
+    public SignatureDto Convert(UnitOfLength unitOfLength)
+    {
+        _unitOfLength = unitOfLength;
+        return this;
+    }
+
+    public double Factor
+    {
+        get
+        {
+            if (SenderAppType != SenderAppType.LegacyFormApp)
+            {
+                throw new NotImplementedException(
+                    $"SenderAppType '{SenderAppType}' is not yet implemented. " +
+                    $"Currently, only '{nameof(SenderAppType.LegacyFormApp)}' is supported. " +
+                    $"Future implementations will handle '{nameof(SenderAppType.ReceiverUIBlazorApp)}' and other types.");
+            }
+
+            // LegacyFormApp uses GdPicture14 with INCHES
+            return _unitOfLength switch
+            {
+                UnitOfLength.Inch => 1.0,   // No conversion needed: INCHES ? INCHES
+                UnitOfLength.Point => 72.0, // INCHES ? PDF Points: 1 inch = 72 points (PDF standard, NOT pixels!)
+                _ => throw new InvalidOperationException(
+                    $"Unknown UnitOfLength: {_unitOfLength}. Expected '{nameof(UnitOfLength.Inch)}' or '{nameof(UnitOfLength.Point)}'.")
+            };
+        }
+    }
+}
+
+public static class SignatureDtoExtensions
+{
+    /// <summary>
+    /// Converts all signatures in the collection to the specified unit of length.
+    /// </summary>
+    /// <typeparam name="T">Type of the collection (IEnumerable, List, etc.)</typeparam>
+    /// <param name="signatures">Collection of SignatureDto objects to convert.</param>
+    /// <param name="unitOfLength">Target unit of measurement (Inch or Point).</param>
+    /// <returns>The same collection with all signatures converted to the specified unit.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when signatures collection is null.</exception>
+    /// <remarks>
+    /// <b>Usage:</b>
+    /// <code>
+    /// var signatures = await SignatureService.GetAsync(envelopeKey);
+    /// var convertedSignatures = signatures.ConvertAll(UnitOfLength.Point);
+    /// </code>
+    /// <b>Note:</b> This method modifies each SignatureDto object in place and returns the same collection.
+    /// </remarks>
+    public static T Convert<T>(this T signatures, UnitOfLength unitOfLength) 
+        where T : IEnumerable<SignatureDto>
+    {
+        if (signatures == null)
+            throw new ArgumentNullException(nameof(signatures));
+
+        foreach (var signature in signatures)
+        {
+            signature.Convert(unitOfLength);
+        }
+
+        return signatures;
+    }
+}