Fix admin sidebar missing on /curator/* routes

- Extract AdminShell component (sidebar + wrapper)
- admin/layout.tsx uses AdminShell
- curator/layout.tsx uses AdminShell for admin role (was rendering children only)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/admin/admin-shell.tsx

@@ -0,0 +1,40 @@
+import { AdminNav } from "@/components/admin/admin-nav";
+import { LogoutButton } from "@/components/layout/logout-button";
+
+export function AdminShell({
+  children,
+  userName,
+}: {
+  children: React.ReactNode;
+  userName: string;
+}) {
+  return (
+    <div className="min-h-screen flex">
+      <aside
+        className="w-52 flex flex-col shrink-0 fixed h-full z-10"
+        style={{ backgroundColor: "var(--sidebar-bg)", color: "var(--sidebar-text)" }}
+      >
+        <div className="px-5 py-5" style={{ borderBottom: "2px solid var(--sidebar-border)" }}>
+          <p className="font-bold text-base tracking-wide" style={{ color: "#E8F0D8" }}>
+            Second Brain
+          </p>
+          <p className="text-xs mt-0.5 uppercase tracking-widest" style={{ color: "var(--sidebar-text)", fontSize: "0.6rem" }}>
+            Администратор
+          </p>
+        </div>
+        <nav className="flex-1 px-2 py-4 space-y-0.5 overflow-y-auto">
+          <AdminNav />
+        </nav>
+        <div className="px-4 py-4" style={{ borderTop: "2px solid var(--sidebar-border)" }}>
+          <p className="text-xs mb-3 truncate" style={{ color: "var(--sidebar-text)" }}>
+            {userName}
+          </p>
+          <LogoutButton />
+        </div>
+      </aside>
+      <div className="ml-52 flex-1 min-h-screen" style={{ backgroundColor: "var(--background)" }}>
+        {children}
+      </div>
+    </div>
+  );
+}