Add EnvelopeReceiverDto and related service class

Introduced `EnvelopeReceiverDto` and its nested models (`EnvelopeClientDto`, `EnvelopeSenderDto`, `DocumentClientDto`, `SignatureClientDto`, `ReceiverClientDto`) to represent client-side data for envelope receivers and their associated entities.

Added `EnvelopeReceiverService` to fetch `EnvelopeReceiverDto` from the API using `HttpClient`. Implemented error handling and JSON deserialization with `JsonSerializerDefaults.Web`. Updated necessary `using` directives.

EnvelopeGenerator.ReceiverUI/Models/EnvelopeReceiverDto.cs

@@ -0,0 +1,106 @@
+namespace EnvelopeGenerator.ReceiverUI.Models;
+
+/// <summary>
+/// Client-side model for the envelope receiver returned by
+/// <c>GET api/EnvelopeReceiver/{envelopeKey}</c>.
+/// </summary>
+public record EnvelopeReceiverDto
+{
+    public int EnvelopeId { get; init; }
+    public int ReceiverId { get; init; }
+    public int Sequence { get; init; }
+
+    public string? Name { get; init; }
+    public string? JobTitle { get; init; }
+    public string? CompanyName { get; init; }
+    public string? PrivateMessage { get; init; }
+
+    public DateTime AddedWhen { get; init; }
+    public DateTime? ChangedWhen { get; init; }
+    public bool HasPhoneNumber { get; init; }
+
+    public EnvelopeClientDto? Envelope { get; init; }
+    public ReceiverClientDto? Receiver { get; init; }
+}
+
+/// <summary>
+/// Client-side model for the envelope data embedded in <see cref="EnvelopeReceiverDto"/>.
+/// </summary>
+public record EnvelopeClientDto
+{
+    public int Id { get; init; }
+    public int UserId { get; init; }
+    public int Status { get; init; }
+    public string StatusName { get; init; } = string.Empty;
+    public string Uuid { get; init; } = string.Empty;
+    public string Title { get; init; } = string.Empty;
+    public string Message { get; init; } = string.Empty;
+    public DateTime AddedWhen { get; init; }
+    public DateTime? ChangedWhen { get; init; }
+    public string Language { get; init; } = "de-DE";
+    public int? EnvelopeTypeId { get; init; }
+    public string? EnvelopeTypeTitle { get; init; }
+    public int? ContractType { get; init; }
+    public int? CertificationType { get; init; }
+    public bool UseAccessCode { get; init; }
+    public bool TFAEnabled { get; init; }
+    public IEnumerable<DocumentClientDto>? Documents { get; init; }
+    public EnvelopeSenderDto? User { get; init; }
+}
+
+/// <summary>
+/// Sender (user) information embedded in <see cref="EnvelopeClientDto"/>.
+/// </summary>
+public record EnvelopeSenderDto
+{
+    public int Id { get; init; }
+    public string? Username { get; init; }
+    public string? FullName { get; init; }
+    public string? Email { get; init; }
+}
+
+/// <summary>
+/// Client-side model for a document embedded in <see cref="EnvelopeClientDto"/>.
+/// </summary>
+public record DocumentClientDto
+{
+    public int Id { get; init; }
+    public int EnvelopeId { get; init; }
+    public DateTime AddedWhen { get; init; }
+    public IEnumerable<SignatureClientDto>? Elements { get; init; }
+}
+
+/// <summary>
+/// Client-side model for a signature/annotation element embedded in <see cref="DocumentClientDto"/>.
+/// </summary>
+public record SignatureClientDto
+{
+    public int Id { get; init; }
+    public int DocumentId { get; init; }
+    public int ReceiverId { get; init; }
+    public int ElementType { get; init; }
+    public double X { get; init; }
+    public double Y { get; init; }
+    public double Width { get; init; }
+    public double Height { get; init; }
+    public int Page { get; init; }
+    public bool Required { get; init; }
+    public string? Tooltip { get; init; }
+    public bool ReadOnly { get; init; }
+    public int AnnotationIndex { get; init; }
+    public DateTime AddedWhen { get; init; }
+    public DateTime? ChangedWhen { get; init; }
+}
+
+/// <summary>
+/// Client-side model for the receiver data embedded in <see cref="EnvelopeReceiverDto"/>.
+/// </summary>
+public record ReceiverClientDto
+{
+    public int Id { get; init; }
+    public string? EmailAddress { get; init; }
+    public string? Signature { get; init; }
+    public DateTime AddedWhen { get; init; }
+    public DateTime? TfaRegDeadline { get; init; }
+}
+

EnvelopeGenerator.ReceiverUI/Services/EnvelopeReceiverService.cs

@@ -0,0 +1,27 @@
+using System.Net.Http.Json;
+using System.Text.Json;
+using EnvelopeGenerator.ReceiverUI.Models;
+using EnvelopeGenerator.ReceiverUI.Options;
+using Microsoft.Extensions.Options;
+
+namespace EnvelopeGenerator.ReceiverUI.Services;
+
+/// <summary>
+/// Retrieves the <see cref="EnvelopeReceiverDto"/> for the authenticated receiver
+/// from <c>GET api/EnvelopeReceiver/{envelopeKey}</c>.
+/// </summary>
+public class EnvelopeReceiverService(HttpClient http, IOptions<ApiOptions> apiOptions)
+{
+    private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
+
+    public async Task<EnvelopeReceiverDto?> GetAsync(string envelopeKey, CancellationToken cancel = default)
+    {
+        var url = $"{apiOptions.Value.BaseUrl}/api/EnvelopeReceiver/{Uri.EscapeDataString(envelopeKey)}";
+        var response = await http.GetAsync(url, cancel);
+
+        if (!response.IsSuccessStatusCode)
+            return null;
+
+        return await response.Content.ReadFromJsonAsync<EnvelopeReceiverDto>(_jsonOptions, cancel);
+    }
+}