Add envelope receiver access code request feature

Introduced a feature to allow envelope receivers to request an
access code via email on the login page.

- Added `OnInitializedAsync` in `LoginReceiverPage.razor` to
  trigger access code requests using `AuthService`.
- Implemented `RequestEnvelopeReceiverAccessCodeAsync` in
  `AuthService.cs` to handle API calls for access code requests.
- Added a new endpoint in `AuthController` to process access
  code requests, including validation, history recording, and
  email dispatching.
- Registered `IEnvelopeMailService` and `AddDispatcher` in
  `Program.cs` to support email dispatch and database operations.
- Refactored `AuthController` constructor for readability and
  added necessary `using` directives.
- Improved logging and error handling for better traceability
  and robustness.

These changes ensure a seamless and secure process for envelope
receivers to request access codes, enhancing the user experience.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/LoginReceiverPage.razor

@@ -144,6 +144,14 @@
     bool IsLoading;
     EnvelopeLoginResult? LoginResult;
 
+    protected override async Task OnInitializedAsync()
+    {
+        if (string.IsNullOrWhiteSpace(EnvelopeKey))
+            return;
+
+        _ = await AuthService.RequestEnvelopeReceiverAccessCodeAsync(EnvelopeKey);
+    }
+
     async Task OnKeyDownAsync(Microsoft.AspNetCore.Components.Web.KeyboardEventArgs e)
     {
         if (e.Key == "Enter")

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

@@ -33,6 +33,20 @@ public class AuthService(IHttpClientFactory httpClientFactory)
         return response.StatusCode == HttpStatusCode.OK;
     }
 
+    /// <summary>
+    /// Triggers access code e-mail request flow for the receiver login page.
+    /// Calls POST /api/Auth/envelope-receiver/{key}/request-access-code.
+    /// </summary>
+    public async Task<bool> RequestEnvelopeReceiverAccessCodeAsync(string envelopeKey, CancellationToken cancel = default)
+    {
+        using var http = CreateDefaultClient();
+        var response = await http.PostAsync(
+            $"/api/Auth/envelope-receiver/{Uri.EscapeDataString(envelopeKey)}/request-access-code",
+            null,
+            cancel);
+        return response.IsSuccessStatusCode;
+    }
+
     /// <summary>
     /// Submits the access code for the given envelope key.
     /// Calls POST /api/Auth/envelope-receiver/{key} with multipart/form-data.