feat(admin): add IA shell and protected section skeleton routes

apps/admin/src/components/admin-section-placeholder.tsx

@@ -0,0 +1,40 @@
+import type { ReactNode } from "react"
+
+type AdminSectionPlaceholderProps = {
+  feature: string
+  summary: string
+  requiredPermission: string
+  nextSteps: string[]
+  children?: ReactNode
+}
+
+export function AdminSectionPlaceholder({
+  feature,
+  summary,
+  requiredPermission,
+  nextSteps,
+  children,
+}: AdminSectionPlaceholderProps) {
+  return (
+    <section className="space-y-5 rounded-xl border border-neutral-200 p-6">
+      <div className="space-y-2">
+        <h2 className="text-xl font-medium">{feature}</h2>
+        <p className="text-sm text-neutral-600">{summary}</p>
+        <p className="text-xs uppercase tracking-wide text-neutral-500">
+          Required permission: {requiredPermission}
+        </p>
+      </div>
+
+      {children}
+
+      <div className="rounded-lg border border-neutral-200 bg-neutral-50 p-4">
+        <p className="text-sm font-medium text-neutral-800">Planned next steps</p>
+        <ul className="mt-2 list-disc space-y-1 pl-5 text-sm text-neutral-600">
+          {nextSteps.map((step) => (
+            <li key={step}>{step}</li>
+          ))}
+        </ul>
+      </div>
+    </section>
+  )
+}