feat(sender): add envelope delete popup and client call

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/EnvelopeService.cs

@@ -12,6 +12,8 @@ namespace EnvelopeGenerator.Server.Client.Services;
 public class EnvelopeService(IHttpClientFactory clientFactory)
 {
     private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
+    private sealed record DeleteEnvelopeRequest(string Reason);
+    private sealed record ErrorResponse(string? Message);
 
     /// <summary>
     /// Fetches envelopes from the API with optional filters.
@@ -61,4 +63,35 @@ public class EnvelopeService(IHttpClientFactory clientFactory)
 
         return await response.Content.ReadFromJsonAsync<IEnumerable<EnvelopeDto>>(_jsonOptions, cancel);
     }
+
+    public async Task DeleteAsync(int envelopeId, string reason, CancellationToken cancel = default)
+    {
+        var httpClient = clientFactory.CreateClient("EnvelopeGenerator.Server");
+        using var request = new HttpRequestMessage(HttpMethod.Delete, $"/api/Envelope/{envelopeId}")
+        {
+            Content = JsonContent.Create(new DeleteEnvelopeRequest(reason), options: _jsonOptions)
+        };
+
+        var response = await httpClient.SendAsync(request, cancel);
+        if (response.IsSuccessStatusCode)
+            return;
+
+        string? message = null;
+        try
+        {
+            var error = await response.Content.ReadFromJsonAsync<ErrorResponse>(_jsonOptions, cancel);
+            message = error?.Message;
+        }
+        catch
+        {
+            message = null;
+        }
+
+        var statusCode = (int)response.StatusCode;
+        var reasonPhrase = response.ReasonPhrase ?? "Unknown error";
+        throw new HttpRequestException(
+            $"Failed to delete envelope. Status: {statusCode} ({reasonPhrase}){(string.IsNullOrWhiteSpace(message) ? string.Empty : $" - {message}")}",
+            null,
+            response.StatusCode);
+    }
 }