Add logout functionality and signed status check

Introduced a logout feature to the `ReceiverPage` component:
- Added a logout button to the toolbar with `_isLoggingOut` state.
- Implemented `LogoutAsync` method to handle logout logic, including navigation and error handling.
- Injected `IMediator` and `ILogger<ReceiverPage>` for logging and MediatR functionality.
- Added a check in `OnInitializedAsync` to redirect users to `/envelope/signed-result` if the envelope is already signed.
- Updated namespaces to include MediatR and custom extensions.

These changes improve user experience and enhance the component's functionality.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Components/Pages/ReceiverPage.razor

@@ -6,11 +6,14 @@
 @using EnvelopeGenerator.Server.Client.Models.Constants
 @using EnvelopeGenerator.Server.Client.Services
 @using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver
+@using EnvelopeGenerator.Application.EnvelopeReceivers.Queries
 @using Microsoft.JSInterop
 @using DevExpress.Blazor
 @using System.Drawing
 @using System.Security.Claims
 @using Microsoft.Extensions.Caching.Memory
+@using MediatR
+@using EnvelopeGenerator.Server.Extensions
 @inject NavigationManager Navigation
 @inject IJSRuntime JSRuntime
 @inject EnvelopeGenerator.Server.Client.Services.AuthService AuthService
@@ -19,6 +22,7 @@
 @inject AppVersionService AppVersion
 @inject IMemoryCache MemoryCache
 @inject ILogger<ReceiverPage> Logger
+@inject IMediator Mediator
 @implements IDisposable
 
 <link href="_content/DevExpress.Blazor.Themes/blazing-berry.bs5.min.css" rel="stylesheet" />
@@ -125,6 +129,18 @@
                             <span class="pdf-toolbar__btn-text">Unterschreiben</span>
                         </button>
                     }
+
+                    <button class="pdf-toolbar__btn"
+                            @onclick="LogoutAsync"
+                            disabled="@_isLoggingOut"
+                            title="Abmelden"
+                            style="flex-shrink: 0;">
+                        <svg xmlns="http://www.w3.org/2000/svg" width="14" height="14" fill="currentColor" viewBox="0 0 16 16">
+                            <path fill-rule="evenodd" d="M10 15a1 1 0 0 0 1-1v-2a.5.5 0 0 1 1 0v2a2 2 0 0 1-2 2H3a2 2 0 0 1-2-2V2a2 2 0 0 1 2-2h7a2 2 0 0 1 2 2v2a.5.5 0 0 1-1 0V2a1 1 0 0 0-1-1H3a1 1 0 0 0-1 1v12a1 1 0 0 0 1 1h7z" />
+                            <path fill-rule="evenodd" d="M15.854 8.354a.5.5 0 0 0 0-.708l-3-3a.5.5 0 1 0-.708.708L14.293 7.5H6.5a.5.5 0 0 0 0 1h7.793l-2.147 2.146a.5.5 0 0 0 .708.708l3-3z" />
+                        </svg>
+                        <span class="pdf-toolbar__btn-text">@(_isLoggingOut ? "Abmelden..." : "Abmelden")</span>
+                    </button>
                 </div>
             </div>
 
@@ -386,6 +402,27 @@
     string _signerFullName         = string.Empty;
     string _signerPosition         = string.Empty;
     string _signaturePlace         = string.Empty;
+    bool _isLoggingOut             = false;
+
+    async Task LogoutAsync()
+    {
+        if (_isLoggingOut || string.IsNullOrWhiteSpace(EnvelopeKey))
+            return;
+
+        _isLoggingOut = true;
+        await InvokeAsync(StateHasChanged);
+
+        try
+        {
+            await AuthService.LogoutEnvelopeReceiverAsync(EnvelopeKey);
+        }
+        catch (Exception ex)
+        {
+            Logger.LogWarning(ex, "Receiver logout failed for {EnvelopeKey}", EnvelopeKey);
+        }
+
+        Navigation.NavigateTo($"/envelope/login/{Uri.EscapeDataString(EnvelopeKey)}", forceLoad: true);
+    }
 
     // ----- Lifecycle -----
     protected override async Task OnInitializedAsync()
@@ -405,6 +442,12 @@
             return;
         }
 
+        if (await Mediator.IsSignedAsync(_receiverUser.EnvelopeUuid(), _receiverUser.ReceiverSignature()))
+        {
+            Navigation.NavigateTo("/envelope/signed-result", forceLoad: true);
+            return;
+        }
+
         try
         {
             // Load PDF bytes via MediatR (uses authenticated user's claims)