Add localization and UI updates for receiver actions

Added new localized strings for "Recently used recipients" and
"Skip" in German, English, and French resource files. Updated
the `CreateEnvelopeWizardPopup.razor` to enhance the "Add
Receiver" button with a primary render style and a new CSS
class. Introduced styles for the button in `sender-page.css`
to improve its appearance with a minimum width, bold font,
and box shadow.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/css/sender-page.css

@@ -1271,6 +1271,12 @@
     justify-content: flex-end;
 }
 
+.sender-create-wizard__add-receiver-btn.dxbl-btn {
+    min-width: 210px;
+    font-weight: 700;
+    box-shadow: 0 8px 18px rgba(14, 116, 144, 0.22);
+}
+
 .sender-create-wizard__suggestions {
     display: flex;
     flex-direction: column;