Add envelope rejection feature with popup UI

Introduced a new feature to allow users to reject envelopes with an optional reason. Added a `RejectAsync` method in `AnnotationService` to handle rejection requests. Updated `ReceiverPage.razor` to include a "Reject" button in the PDF toolbar and a rejection popup for user input.

Implemented state management for the rejection popup, including visibility, submission status, and validation messages. Updated `AnnotationController` to accept `envelopeKey` as a route parameter for the rejection endpoint. Modified `ReceiverClaimExtensions` to support multiple email claim types.

Added new CSS styles for the "Reject" button, including hover effects and dark theme support. Enhanced error handling and logging for the rejection process.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AnnotationService.cs

@@ -26,4 +26,24 @@ public class AnnotationService(IHttpClientFactory httpClientFactory)
         var result = await response.Content.ReadFromJsonAsync<List<AnnotationDto>>(_jsonOptions, cancel);
         return result ?? [];
     }
+
+    public async Task RejectAsync(string envelopeKey, string? reason, CancellationToken cancel = default)
+    {
+        using var http = httpClientFactory.CreateClient("EnvelopeGenerator.Server");
+
+        var response = await http.PostAsJsonAsync(
+            $"/api/Annotation/reject/{Uri.EscapeDataString(envelopeKey)}",
+            reason,
+            _jsonOptions,
+            cancel);
+
+        if (!response.IsSuccessStatusCode)
+        {
+            var body = await response.Content.ReadAsStringAsync(cancel);
+            throw new HttpRequestException(
+                $"Failed to reject envelope {envelopeKey}: {(int)response.StatusCode} {response.StatusCode} - {body}",
+                null,
+                response.StatusCode);
+        }
+    }
 }