refactor(HomeController): remove culture binding as viewdata; bind via string localizer

EnvelopeGenerator.Web/Views/Shared/_Layout.cshtml

@@ -3,9 +3,6 @@
 @using Newtonsoft.Json.Serialization
 @{
     var nonce = _accessor.HttpContext?.Items["csp-nonce"] as string;
-    var userCulture = ViewData["UserCulture"] as Culture;
-    //TODO: instead of default assignment add a middleware for culture
-    userCulture ??= _cultures.Default;
     var isReadOnly = false;
     if (ViewData["IsReadOnly"] is bool isReadOnly_bool)
         isReadOnly = isReadOnly_bool;
@@ -83,7 +80,7 @@
         <span>&copy; SignFlow 2023-2024 <a href="https://digitaldata.works" target="_blank">Digital Data GmbH</a></span>
         <div class="dropup flag-dropdown">
             <button class="btn btn-outline-secondary dropdown-toggle" type="button" id="langDropdownMenuButton" data-bs-toggle="dropdown" aria-expanded="false">
-                <span class="fi @userCulture?.FIClass.TrySanitize(_sanitizer) me-2" id="selectedFlag"></span><span id="selectedLanguage"></span>
+                <span class="fi @_localizer.FiClass() me-2" id="selectedFlag"></span><span id="selectedLanguage"></span>
             </button>
             <ul class="dropdown-menu" aria-labelledby="langDropdownMenuButton">
                 @foreach (var culture in _cultures)
@@ -98,7 +95,7 @@
                 }
             </ul>
         </div>
-        <a href="/privacy-policy.@(userCulture?.Language).html" target="_blank">@_localizer[WebKey.Privacy]</a>
+        <a href="/privacy-policy.@(_localizer.Culture()).html" target="_blank">@_localizer[WebKey.Privacy]</a>
     </footer>
 </body>
 </html>