Add SaaS frontend code (#5879)

# Description of Changes
Adds the code for the SaaS frontend as proprietary code to the OSS repo.
This version of the code is adapted from 22/1/2026, which was the last
SaaS version based on the 'V2' design. This will move us closer to being
able to have the OSS products understand whether the user has a SaaS
account, and provide the correct UI in those cases.

frontend/src/core/styles/tailwind.css

@@ -13,3 +13,13 @@
 @layer utilities {
   @tailwind utilities;
 }
+
+@layer utilities {
+  .no-scrollbar::-webkit-scrollbar {
+    display: none;
+  }
+  .no-scrollbar {
+    -ms-overflow-style: none; /* IE and Edge */
+    scrollbar-width: none; /* Firefox */
+  }
+}