Refactor sender page and auth service logic

- Added project reference to `EnvelopeGenerator.Application` in the client project.
- Updated imports and injected services in `EnvelopeSenderPage.razor`.
- Improved null handling for `EnvelopeReceivers` and updated email display logic.
- Replaced `CheckSenderAsync` with `CheckSenderAccessAsync` for authorization.
- Refactored `GetStatusInfo` to use `EnvelopeStatus` enum directly.
- Added `CheckSenderAccessAsync` and `LogoutSenderAsync` methods in `AuthService`.
- Simplified `Logout` logic in `AuthController` to remove redundant checks.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Services/AuthService.cs

@@ -22,6 +22,17 @@ public class AuthService(IHttpClientFactory httpClientFactory)
         return response.StatusCode == HttpStatusCode.OK;
     }
 
+    /// <summary>
+    /// Checks whether the current user holds a valid receiver token for the given envelope key.
+    /// Calls GET /api/auth/check/envelope/{envelopeKey}.
+    /// </summary>
+    public async Task<bool> CheckSenderAccessAsync(CancellationToken cancel = default)
+    {
+        using var http = CreateDefaultClient();
+        var response = await http.GetAsync($"/api/auth/check", cancel);
+        return response.StatusCode == HttpStatusCode.OK;
+    }
+
     /// <summary>
     /// Submits the access code for the given envelope key.
     /// Calls POST /api/Auth/envelope-receiver/{key} with multipart/form-data.
@@ -61,6 +72,19 @@ public class AuthService(IHttpClientFactory httpClientFactory)
         return response.IsSuccessStatusCode;
     }
 
+    /// <summary>
+    /// Removes the per-envelope receiver cookie for the given envelope key.
+    /// Calls POST /api/auth/logout/envelope/{envelopeKey}.
+    /// </summary>
+    public async Task<bool> LogoutSenderAsync(CancellationToken cancel = default)
+    {
+        using var http = CreateDefaultClient();
+        var response = await http.PostAsync(
+            $"/api/auth/logout",
+            null, cancel);
+        return response.IsSuccessStatusCode;
+    }
+
     /// <summary>
     /// Authenticates a sender user with username and password.
     /// Calls POST /api/auth?cookie=true with JSON body.