Add localization for cookie consent modal

Added localized strings for the cookie consent modal in de-DE, en-US, and fr-FR resource files. Updated _CookieConsentPartial.cshtml to use these resources for the modal title, message, and accept button, enabling multilingual support. Injected IStringLocalizer to support string localization in the view.

EnvelopeGenerator.Web/Views/Shared/_CookieConsentPartial.cshtml

@@ -1,4 +1,5 @@
 @using Microsoft.AspNetCore.Http.Features
+@inject IStringLocalizer<SharedResource> _localizer
 
 @{
     var nonce = _accessor.HttpContext?.Items["csp-nonce"] as string;
@@ -13,13 +14,13 @@
         <div class="modal-dialog">
             <div class="modal-content">
                 <div class="modal-header">
-                    <h1 class="modal-title fs-5" id="staticBackdropLabel">Datenschutzhinweis</h1>
+                    <h1 class="modal-title fs-5" id="staticBackdropLabel">@_localizer["PrivacyNotice"]</h1>
                 </div>
                 <div class="modal-body">
-                    Wir verwenden technisch notwendige Session Cookies. Diese Cookies sind für den ordnungsgemäßen Betrieb dieser Webseite von nöten und können aus diesm Grund nicht abgewählt werden. Es findet keine Übermittlung an Dritte statt.
+                    @_localizer["CookieConsentMessage"]
                 </div>
                 <div class="modal-footer">
-                    <button type="button" class="btn btn-secondary accept-policy close" data-bs-dismiss="modal" data-cookie-string="@cookieString"><span aria-hidden="true">Accept</span></button>
+                    <button type="button" class="btn btn-secondary accept-policy close" data-bs-dismiss="modal" data-cookie-string="@cookieString"><span aria-hidden="true">@_localizer["Accept"]</span></button>
                 </div>
             </div>
         </div>