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/saas/components/feedback/UserbackWidget.tsx

@@ -0,0 +1,57 @@
+import { useEffect, useRef } from 'react';
+import Userback from '@userback/widget';
+import { useAuth } from '@app/auth/UseSession';
+
+interface UserbackWidgetProps {
+  token: string;
+}
+
+interface UserbackInstance {
+  destroy: () => void;
+}
+
+export default function UserbackWidget({ token }: UserbackWidgetProps) {
+  const { user } = useAuth();
+  const userbackRef = useRef<UserbackInstance | null>(null);
+  const initializingRef = useRef(false);
+
+  useEffect(() => {
+    if (!user || initializingRef.current) return;
+
+    initializingRef.current = true;
+
+    const initializeUserback = async () => {
+      try {
+        // Prepare user data options
+        const userInfo: { name?: string; email?: string } = {};
+        if (user.user_metadata?.full_name) userInfo.name = user.user_metadata.full_name;
+        if (user.email) userInfo.email = user.email;
+
+        const options = {
+          user_data: {
+            id: user.id,
+            info: userInfo
+          }
+        };
+
+        // Initialize Userback
+        userbackRef.current = await Userback(token, options);
+      }
+     finally {
+        initializingRef.current = false;
+      }
+    };
+
+    initializeUserback();
+
+    // Cleanup function
+    return () => {
+      if (userbackRef.current && typeof userbackRef.current.destroy === 'function') {
+        userbackRef.current.destroy();
+      }
+      initializingRef.current = false;
+    };
+  }, [user, token]);
+
+  return null; // This component doesn't render anything visible
+}