Add signature submission feature and pipeline updates

Introduced a new feature for submitting signatures, including
backend and frontend changes. Added `SignatureSubmitDto` and
`SubmitAsync` in `SignatureService` to handle signature data
submission. Implemented a new `Submit` endpoint in
`SignatureController` to validate and process signature payloads.

Updated pipeline behaviors to include `SaveSignatureBehavior`
and adjusted the execution order. Enhanced query logic in
`EnvelopeReceiverResolutionBehavior` and `SaveSignatureBehavior`
to align with the updated data model.

Refactored `EGDbContext` to improve trigger handling and logging.
Updated `ReceiverSignedPage.razor` to integrate `SignatureService`
and handle submission errors gracefully. Adjusted application
URLs in `launchSettings.json` and added new database triggers
in `appsettings.json`.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Components/Pages/ReceiverSignedPage.razor

@@ -12,6 +12,7 @@
 @inject EnvelopeGenerator.Server.Client.Services.AuthService AuthService
 @inject EnvelopeGenerator.Server.Services.EnvelopeReceiverAuthorizationService ReceiverAuthorizationService
 @inject EnvelopeGenerator.Server.Services.EnvelopeReceiverPageDataService PageDataService
+@inject SignatureService SignatureService
 @inject AppVersionService AppVersion
 @inject IMemoryCache MemoryCache
 @inject ILogger<ReceiverSignedPage> Logger
@@ -122,6 +123,12 @@
                 </p>
             </div>
         </div>
+        @if (!string.IsNullOrWhiteSpace(_submitErrorMessage))
+        {
+            <div class="alert alert-danger mb-0" role="alert" style="font-size: 0.85rem;">
+                @_submitErrorMessage
+            </div>
+        }
     </BodyContentTemplate>
     <FooterContentTemplate>
         <div class="d-flex gap-2 justify-content-end w-100" style="padding: 0.5rem 0;">
@@ -161,17 +168,48 @@
     // ----- Submit / logout state -----
     bool _isLoggingOut        = false;
     bool _submitConfirmVisible = false;
+    string? _submitErrorMessage;
 
     void OpenSubmitConfirmPopup() => _submitConfirmVisible = true;
 
     async Task SubmitAndLogoutAsync()
     {
         if (_isLoggingOut) return;
+
+        if (string.IsNullOrWhiteSpace(EnvelopeKey) || _sig is null)
+            return;
+
         _isLoggingOut = true;
         _submitConfirmVisible = false;
+        _submitErrorMessage = null;
         await InvokeAsync(StateHasChanged);
-        await AuthService.LogoutEnvelopeReceiverAsync(EnvelopeKey!);
-        Navigation.NavigateTo("/", forceLoad: true);
+
+        try
+        {
+            if (_signatures.Count == 0)
+                throw new InvalidOperationException("No signature fields found for receiver.");
+
+            var payload = _signatures.Select(field => new SignatureSubmitDto
+            {
+                Id = field.Id,
+                DataUrl = _sig.DataUrl,
+                FullName = _sig.FullName,
+                Position = string.IsNullOrWhiteSpace(_sig.Position) ? null : _sig.Position,
+                Place = _sig.Place
+            }).ToList();
+
+            await SignatureService.SubmitAsync(EnvelopeKey, payload);
+
+            await AuthService.LogoutEnvelopeReceiverAsync(EnvelopeKey);
+            Navigation.NavigateTo("/", forceLoad: true);
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError(ex, "Failed to finalize signature for {EnvelopeKey}", EnvelopeKey);
+            _submitErrorMessage = "Die Unterschrift konnte nicht abgeschlossen werden. Bitte versuchen Sie es erneut.";
+            _isLoggingOut = false;
+            await InvokeAsync(StateHasChanged);
+        }
     }
 
     protected override async Task OnInitializedAsync()