fix(ui): default guardrails page to first tab for admins, not submitted (#29872)

The Guardrails page hardcoded defaultActiveKey="submitted", so admins
landed on the "Submitted Guardrails" tab (the last of their four tabs)
instead of the primary view. The original intent was for non-admins,
whose only tab is Submitted Guardrails, to default there; admins should
open on their first tab.

Make the default role-aware: admins default to the first tab (Guardrail
Garden), non-admins keep Submitted Guardrails.

ui/litellm-dashboard/src/components/guardrails.tsx

@@ -133,7 +133,7 @@ const GuardrailsPanel: React.FC<GuardrailsPanelProps> = ({ accessToken, userRole
   return (
     <div className="w-full mx-auto flex-auto overflow-y-auto m-8 p-2">
       <Tabs
-        defaultActiveKey="submitted"
+        defaultActiveKey="guardrails"
         items={[
           ...(isAdmin
             ? [