fix: ai onboarding not taking up full height in macos desktop

Author: devvaannsh

src/styles/Extn-AIChatPanel.less

@@ -307,6 +307,8 @@
     background-color: @bc-ai-sidebar-bg;
 
     .ai-onboarding-frame {
+        position: absolute;
+        inset: 0;
         width: 100%;
         height: 100%;
         border: 0;