feat: refactor authentication panels and add AdminOnlyNotice component

frontend/src/app/gateways/page.tsx

@@ -5,7 +5,7 @@ export const dynamic = "force-dynamic";
 import { useMemo, useState } from "react";
 import Link from "next/link";
 
-import { SignInButton, SignedIn, SignedOut, useAuth } from "@/auth/clerk";
+import { SignedIn, SignedOut, useAuth } from "@/auth/clerk";
 import {
   type ColumnDef,
   type SortingState,
@@ -40,6 +40,8 @@ import {
   useGetMyMembershipApiV1OrganizationsMeMemberGet,
 } from "@/api/generated/organizations/organizations";
 import type { GatewayRead } from "@/api/generated/model";
+import { AdminOnlyNotice } from "@/components/auth/AdminOnlyNotice";
+import { SignedOutPanel } from "@/components/auth/SignedOutPanel";
 
 const truncate = (value?: string | null, max = 24) => {
   if (!value) return "—";
@@ -235,14 +237,10 @@ export default function GatewaysPage() {
   return (
     <DashboardShell>
       <SignedOut>
-        <div className="col-span-2 flex min-h-[calc(100vh-64px)] items-center justify-center bg-slate-50 p-10 text-center">
-          <div className="rounded-xl border border-slate-200 bg-white px-8 py-6 shadow-sm">
-            <p className="text-sm text-slate-600">Sign in to view gateways.</p>
-            <SignInButton mode="modal" forceRedirectUrl="/gateways">
-              <Button className="mt-4">Sign in</Button>
-            </SignInButton>
-          </div>
-        </div>
+        <SignedOutPanel
+          message="Sign in to view gateways."
+          forceRedirectUrl="/gateways"
+        />
       </SignedOut>
       <SignedIn>
         <DashboardSidebar />
@@ -275,9 +273,7 @@ export default function GatewaysPage() {
 
           <div className="p-8">
             {!isAdmin ? (
-              <div className="rounded-xl border border-slate-200 bg-white px-6 py-5 text-sm text-slate-600 shadow-sm">
-                Only organization owners and admins can access gateways.
-              </div>
+              <AdminOnlyNotice message="Only organization owners and admins can access gateways." />
             ) : (
               <>
                 <div className="overflow-hidden rounded-xl border border-slate-200 bg-white shadow-sm">