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/AnnotationService.cs

@@ -0,0 +1,33 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+using EnvelopeGenerator.WebUI.Client.Models;
+using EnvelopeGenerator.WebUI.Client.Options;
+using Microsoft.Extensions.Options;
+
+namespace EnvelopeGenerator.WebUI.Client.Services;
+
+/// <summary>
+/// Retrieves annotation positions from the API.
+/// The URL is composed as <c>{BaseUrl}/api/Annotation/{envelopeKey}</c>.
+/// During development, <c>BaseUrl</c> is empty so the request resolves to the
+/// YARP-proxied route on the same origin, which currently serves
+/// <c>fake-data/annotations.json</c>. To switch to real data, update the
+/// YARP route in <c>yarp.json</c> – no code change required.
+/// </summary>
+[Obsolete("Use SignatureService.")]
+public class AnnotationService(HttpClient http, IOptions<ApiOptions> apiOptions)
+{
+    private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
+
+    public async Task<IReadOnlyList<AnnotationDto>> GetAnnotationsAsync(string envelopeKey, CancellationToken cancel = default)
+    {
+        var url = $"{apiOptions.Value.BaseUrl}/api/Annotation/{Uri.EscapeDataString(envelopeKey)}";
+        var response = await http.GetAsync(url, cancel);
+
+        if (!response.IsSuccessStatusCode)
+            return [];
+
+        var result = await response.Content.ReadFromJsonAsync<List<AnnotationDto>>(_jsonOptions, cancel);
+        return result ?? [];
+    }
+}