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);
+    }
 }

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Components/Pages/EnvelopeSenderPage.razor

@@ -521,6 +521,54 @@
     </BodyContentTemplate>
 </DxPopup>
 
+<DxPopup @bind-Visible="@_deletePopupVisible"
+         HeaderText="Umschlag löschen"
+         Width="560px"
+         MaxWidth="95vw"
+         ShowFooter="true"
+         CloseOnOutsideClick="false"
+         ShowCloseButton="true"
+         CloseOnEscape="true"
+         ShowHeader="true"
+         CssClass="sender-delete-popup">
+    <BodyContentTemplate>
+        <div style="display:flex;flex-direction:column;gap:0.75rem;">
+            <p style="margin:0;color:#374151;font-size:0.9rem;line-height:1.45;">
+                Bitte geben Sie einen Grund an, warum der Umschlag gelöscht/zurückgezogen werden soll.
+            </p>
+            @if (_selectedEnvelope is not null)
+            {
+                <p style="margin:0;color:#6b7280;font-size:0.825rem;">
+                    Umschlag: <strong>#@_selectedEnvelope.Id - @_selectedEnvelope.Title</strong>
+                </p>
+            }
+            <DxMemo @bind-Text="_deleteReason"
+                    NullText="Begründung eingeben..."
+                    Rows="5"
+                    MaxLength="2000"
+                    CssClass="w-100" />
+            @if (!string.IsNullOrWhiteSpace(_deleteErrorMessage))
+            {
+                <div class="alert alert-danger" style="margin:0;padding:0.5rem 0.75rem;font-size:0.85rem;">
+                    @_deleteErrorMessage
+                </div>
+            }
+        </div>
+    </BodyContentTemplate>
+    <FooterContentTemplate>
+        <div style="display:flex;justify-content:flex-end;gap:0.5rem;width:100%;">
+            <DxButton Text="Abbrechen"
+                      RenderStyle="ButtonRenderStyle.Secondary"
+                      Click="CloseDeletePopup"
+                      Enabled="@(!_isDeletingEnvelope)" />
+            <DxButton Text="Löschen"
+                      RenderStyle="ButtonRenderStyle.Danger"
+                      Click="ConfirmDeleteEnvelopeAsync"
+                      Enabled="@(!_isDeletingEnvelope)" />
+        </div>
+    </FooterContentTemplate>
+</DxPopup>
+
 @code {
     private IEnumerable<EnvelopeDto>? _allEnvelopes;
     private IEnumerable<EnvelopeDto>? _activeEnvelopes;
@@ -549,6 +597,11 @@
     private bool _exportSelectedRowsOnly = false;
     private bool _isExporting = false;
 
+    private bool _deletePopupVisible = false;
+    private bool _isDeletingEnvelope = false;
+    private string _deleteReason = string.Empty;
+    private string? _deleteErrorMessage;
+
     // Stable keys used to store/restore each grid's layout in UserPreferences.GridLayouts
     private const string GridKeyActive = "sender.active-envelopes";
     private const string GridKeyCompleted = "sender.completed-envelopes";
@@ -681,7 +734,51 @@
     void DeleteEnvelope()
     {
         if (_selectedEnvelope == null) return;
-        // TODO: Show delete confirmation dialog
+        _deleteReason = string.Empty;
+        _deleteErrorMessage = null;
+        _deletePopupVisible = true;
+    }
+
+    void CloseDeletePopup()
+    {
+        if (_isDeletingEnvelope)
+            return;
+
+        _deletePopupVisible = false;
+        _deleteErrorMessage = null;
+    }
+
+    async Task ConfirmDeleteEnvelopeAsync()
+    {
+        if (_selectedEnvelope is null)
+            return;
+
+        if (string.IsNullOrWhiteSpace(_deleteReason))
+        {
+            _deleteErrorMessage = "Bitte geben Sie einen Löschgrund an.";
+            return;
+        }
+
+        _isDeletingEnvelope = true;
+        _deleteErrorMessage = null;
+        await InvokeAsync(StateHasChanged);
+
+        try
+        {
+            await EnvelopeService.DeleteAsync(_selectedEnvelope.Id, _deleteReason.Trim());
+            _deletePopupVisible = false;
+            _selectedEnvelope = null;
+            await LoadEnvelopesAsync();
+        }
+        catch (Exception ex)
+        {
+            _deleteErrorMessage = ex.Message;
+        }
+        finally
+        {
+            _isDeletingEnvelope = false;
+            await InvokeAsync(StateHasChanged);
+        }
     }
 
     async Task LogoutAsync()