Add "Send Confirmation" feature for envelope sending

Introduced a "Send Confirmation" popup to improve user experience
when sending envelopes. The popup allows users to review recipients,
signature fields, and settings before confirming the send action.

- Added localized strings in `Resource.de-DE.resx`, `Resource.en-US.resx`,
  and `Resource.fr-FR.resx` for confirmation messages and actions.
- Updated `SenderEditorPage.razor` to include the confirmation popup
  (`DxPopup`) with body and footer templates.
- Added `RequestSendAsync` and `ConfirmSendAsync` methods to manage
  the confirmation process and sending logic.
- Replaced the old success popup logic with direct navigation to the
  sender dashboard after a successful send.
- Updated the toolbar button to trigger the confirmation popup.
- Styled the confirmation popup in `envelope-viewer.css`, including
  support for dark themes.
- Ensured proper state management for the popup and sending process.

These changes enhance usability by providing a clear confirmation
step and progress feedback during envelope sending.

EnvelopeGenerator.Application/Resources/Resource.de-DE.resx

@@ -751,6 +751,12 @@
   <data name="SenderEditor_RemoveAllSignatureFields" xml:space="preserve"><value>Alle Signaturfelder entfernen</value></data>
   <data name="SenderEditor_RemoveAllSignatureFieldsConfirm" xml:space="preserve"><value>Diese Aktion entfernt alle platzierten Signaturfelder unwiderruflich. Fortfahren?</value></data>
   <data name="SenderEditor_SelectPdf" xml:space="preserve"><value>Bitte wählen Sie eine PDF-Datei aus.</value></data>
+  <data name="SenderEditor_SendConfirm_Message" xml:space="preserve"><value>Wollen Sie den Umschlag jetzt versenden? Hinweis: Nach der Übergabe kann der Vorgang nicht mehr bearbeitet werden.</value></data>
+  <data name="SenderEditor_SendConfirm_Title" xml:space="preserve"><value>Umschlag jetzt versenden?</value></data>
+  <data name="SenderEditor_SendConfirm_Note" xml:space="preserve"><value>Bitte prüfen Sie Empfänger, Signaturfelder und Einstellungen vor dem Versenden.</value></data>
+  <data name="SenderEditor_SendConfirm_Action" xml:space="preserve"><value>Jetzt versenden</value></data>
+  <data name="SenderEditor_SendConfirm_InProgress" xml:space="preserve"><value>Umschlag wird versendet...</value></data>
+  <data name="SenderEditor_SendConfirm_InProgressHint" xml:space="preserve"><value>Bitte warten Sie einen Moment. Der Vorgang wird abgeschlossen.</value></data>
   <data name="SenderEditor_Sent_Body" xml:space="preserve"><value>Der bestehende Entwurf wurde versendet.</value></data>
   <data name="SenderEditor_Sent_Header" xml:space="preserve"><value>Umschlag gesendet</value></data>
   <data name="SenderEditor_Sent_Title" xml:space="preserve"><value>Umschlag wurde erfolgreich gesendet.</value></data>

EnvelopeGenerator.Application/Resources/Resource.en-US.resx

@@ -751,6 +751,12 @@
   <data name="SenderEditor_RemoveAllSignatureFields" xml:space="preserve"><value>Remove all signature fields</value></data>
   <data name="SenderEditor_RemoveAllSignatureFieldsConfirm" xml:space="preserve"><value>This action will permanently remove all placed signature fields. Continue?</value></data>
   <data name="SenderEditor_SelectPdf" xml:space="preserve"><value>Please select a PDF file.</value></data>
+  <data name="SenderEditor_SendConfirm_Message" xml:space="preserve"><value>Do you want to send the envelope now? Note: After handover, the process can no longer be edited.</value></data>
+  <data name="SenderEditor_SendConfirm_Title" xml:space="preserve"><value>Send envelope now?</value></data>
+  <data name="SenderEditor_SendConfirm_Note" xml:space="preserve"><value>Please review recipients, signature fields, and settings before sending.</value></data>
+  <data name="SenderEditor_SendConfirm_Action" xml:space="preserve"><value>Send now</value></data>
+  <data name="SenderEditor_SendConfirm_InProgress" xml:space="preserve"><value>Sending envelope...</value></data>
+  <data name="SenderEditor_SendConfirm_InProgressHint" xml:space="preserve"><value>Please wait a moment while we complete the process.</value></data>
   <data name="SenderEditor_Sent_Body" xml:space="preserve"><value>The existing draft has been sent.</value></data>
   <data name="SenderEditor_Sent_Header" xml:space="preserve"><value>Envelope sent</value></data>
   <data name="SenderEditor_Sent_Title" xml:space="preserve"><value>Envelope was sent successfully.</value></data>

EnvelopeGenerator.Application/Resources/Resource.fr-FR.resx

@@ -751,6 +751,12 @@
   <data name="SenderEditor_RemoveAllSignatureFields" xml:space="preserve"><value>Supprimer tous les champs de signature</value></data>
   <data name="SenderEditor_RemoveAllSignatureFieldsConfirm" xml:space="preserve"><value>Cette action supprimera définitivement tous les champs de signature placés. Continuer?</value></data>
   <data name="SenderEditor_SelectPdf" xml:space="preserve"><value>Veuillez sélectionner un fichier PDF.</value></data>
+  <data name="SenderEditor_SendConfirm_Message" xml:space="preserve"><value>Voulez-vous envoyer l'enveloppe maintenant ? Remarque : après la transmission, le processus ne peut plus être modifié.</value></data>
+  <data name="SenderEditor_SendConfirm_Title" xml:space="preserve"><value>Envoyer l'enveloppe maintenant ?</value></data>
+  <data name="SenderEditor_SendConfirm_Note" xml:space="preserve"><value>Veuillez vérifier les destinataires, les champs de signature et les paramètres avant l'envoi.</value></data>
+  <data name="SenderEditor_SendConfirm_Action" xml:space="preserve"><value>Envoyer maintenant</value></data>
+  <data name="SenderEditor_SendConfirm_InProgress" xml:space="preserve"><value>Envoi de l'enveloppe...</value></data>
+  <data name="SenderEditor_SendConfirm_InProgressHint" xml:space="preserve"><value>Veuillez patienter un instant pendant la finalisation du traitement.</value></data>
   <data name="SenderEditor_Sent_Body" xml:space="preserve"><value>Le brouillon existant a été envoyé.</value></data>
   <data name="SenderEditor_Sent_Header" xml:space="preserve"><value>Enveloppe envoyée</value></data>
   <data name="SenderEditor_Sent_Title" xml:space="preserve"><value>L'enveloppe a été envoyée avec succès.</value></data>

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/SenderEditorPage.razor

@@ -318,7 +318,7 @@
                 </button>
 
                 <button class="pdf-toolbar__btn pdf-toolbar__btn--success"
-                        @onclick="SendAsync"
+                        @onclick="RequestSendAsync"
                         disabled="@_isSaving"
                         title='@L("SendEnvelope", "Umschlag senden")'>
                     @if (_isSaving)
@@ -530,6 +530,46 @@
     </BodyContentTemplate>
 </DxPopup>
 
+@* ── Send confirmation popup ── *@
+<DxPopup @bind-Visible="_sendConfirmVisible"
+         HeaderText='@L("SenderEditor_SendConfirm_Title", "Umschlag jetzt versenden?")'
+         SizeMode="SizeMode.Medium"
+         Width="460px"
+         MaxWidth="95vw"
+         ShowFooter="@(!_isSendConfirmSubmitting)"
+         ShowCloseButton="@(!_isSendConfirmSubmitting)"
+         CloseOnEscape="@(!_isSendConfirmSubmitting)"
+         CloseOnOutsideClick="false">
+    <BodyContentTemplate>
+        @if (_isSendConfirmSubmitting)
+        {
+            <div class="sender-send-progress">
+                <DxWaitIndicator Visible="true" />
+                <div>
+                    <p class="sender-send-progress__title">@L("SenderEditor_SendConfirm_InProgress", "Umschlag wird versendet...")</p>
+                    <p class="sender-send-progress__hint">@L("SenderEditor_SendConfirm_InProgressHint", "Bitte warten Sie einen Moment. Der Vorgang wird abgeschlossen.")</p>
+                </div>
+            </div>
+        }
+        else
+        {
+            <div class="sender-confirm-popup sender-confirm-popup--send">
+                <p class="sender-confirm-popup__note">
+                    @L("SenderEditor_SendConfirm_Message", "Wollen Sie den Umschlag jetzt versenden? Hinweis: Nach der Übergabe kann der Vorgang nicht mehr bearbeitet werden.")
+                </p>
+            </div>
+        }
+    </BodyContentTemplate>
+    <FooterContentTemplate>
+        <DxButton Text='@L("No", "Nein")'
+                  RenderStyle="ButtonRenderStyle.Secondary"
+                  Click='() => _sendConfirmVisible = false' />
+        <DxButton Text='@L("SenderEditor_SendConfirm_Action", "Ja, versenden")'
+                  RenderStyle="ButtonRenderStyle.Primary"
+                  Click="ConfirmSendAsync" />
+    </FooterContentTemplate>
+</DxPopup>
+
 @* ── Save result popup (success + error) ── *@
 <DxPopup @bind-Visible="_savePopupVisible"
          HeaderText='@(_saveErrorMessage is null ? _saveSuccessHeader : L("Error", "Fehler"))'
@@ -645,6 +685,8 @@
     bool _isSaving = false;
     bool _savePopupVisible = false;
     bool _clearFieldsConfirmVisible = false;
+    bool _sendConfirmVisible = false;
+    bool _isSendConfirmSubmitting = false;
     string? _saveErrorMessage = null;
     string _saveSuccessHeader = "Erfolg";
     string _saveSuccessTitle = "Vorgang erfolgreich abgeschlossen.";
@@ -1241,13 +1283,7 @@
 
             Logger.LogInformation("[SenderEditor] Envelope sent from draft. Id={Id} Status={Status}", sendResult.Id, sendResult.Status);
 
-            // Success — show popup; GoToDashboard clears cache and navigates
-            _saveErrorMessage = null;
-            _saveSuccessHeader = L("SenderEditor_Sent_Header", "Umschlag gesendet");
-            _saveSuccessTitle = L("SenderEditor_Sent_Title", "Umschlag wurde erfolgreich gesendet.");
-            _saveSuccessBody = L("SenderEditor_Sent_Body", "Der bestehende Entwurf wurde versendet.");
-            _saveNavigateToDashboard = true;
-            _savePopupVisible = true;
+            NavigationManager.NavigateTo("/sender", forceLoad: false);
         }
         catch (Exception ex)
         {
@@ -1261,6 +1297,38 @@
         }
     }
 
+    Task RequestSendAsync()
+    {
+        if (_isSaving)
+            return Task.CompletedTask;
+
+        _sendConfirmVisible = true;
+        return Task.CompletedTask;
+    }
+
+    async Task ConfirmSendAsync()
+    {
+        if (_isSendConfirmSubmitting)
+            return;
+
+        _isSendConfirmSubmitting = true;
+        await InvokeAsync(StateHasChanged);
+
+        try
+        {
+            await SendAsync();
+        }
+        finally
+        {
+            _isSendConfirmSubmitting = false;
+
+            if (_savePopupVisible)
+                _sendConfirmVisible = false;
+
+            await InvokeAsync(StateHasChanged);
+        }
+    }
+
     CreateEnvelopeCommand BuildCreateEnvelopeCommand(bool send)
     {
         NormalizeSettings();

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/css/envelope-viewer.css

@@ -2103,3 +2103,61 @@ body.resizing {
     gap: 0.5rem;
     justify-content: flex-end;
 }
+
+.sender-confirm-popup--send {
+    padding: 0.5rem 0.25rem;
+}
+
+.sender-confirm-popup--send .sender-confirm-popup__note {
+    margin: 0;
+    text-align: center;
+}
+
+.sender-confirm-popup__title {
+    margin: 0 0 0.4rem;
+    font-size: 1.02rem;
+    font-weight: 600;
+    color: #0f172a;
+}
+
+.sender-confirm-popup__note {
+    margin: 0 0 1rem;
+    font-size: 0.84rem;
+    color: #475569;
+}
+
+.sender-send-progress {
+    display: flex;
+    align-items: center;
+    gap: 0.75rem;
+    padding: 0.5rem 0.25rem;
+}
+
+.sender-send-progress__spinner {
+    width: 1.15rem;
+    height: 1.15rem;
+    color: #2563eb;
+}
+
+.sender-send-progress__title {
+    margin: 0 0 0.2rem;
+    font-size: 0.95rem;
+    font-weight: 600;
+    color: #0f172a;
+}
+
+.sender-send-progress__hint {
+    margin: 0;
+    font-size: 0.83rem;
+    color: #475569;
+}
+
+[data-sf-theme="blazing-dark"] .sender-confirm-popup__title,
+[data-sf-theme="blazing-dark"] .sender-send-progress__title {
+    color: #e2e8f0;
+}
+
+[data-sf-theme="blazing-dark"] .sender-confirm-popup__note,
+[data-sf-theme="blazing-dark"] .sender-send-progress__hint {
+    color: #94a3b8;
+}