feat: add local auth billing and usage management

app/billing/error.tsx

@@ -0,0 +1,20 @@
+"use client";
+
+import { useEffect } from "react";
+
+export default function BillingError({ reset }: { error: Error & { digest?: string }; reset: () => void }) {
+  useEffect(() => {
+    // Keep the error boundary intentionally quiet in production; the API/log layer records the server cause.
+  }, []);
+
+  return (
+    <main className="billing-route-error">
+      <div className="billing-route-error-card">
+        <span className="billing-route-error-kicker">计费中心</span>
+        <h1>计费服务暂时不可用</h1>
+        <p>请先刷新页面。如果平台使用 Supabase，请确认已在 SQL Editor 执行最新的 <code>supabase/schema.sql</code>。</p>
+        <button type="button" onClick={() => reset()}>重新加载</button>
+      </div>
+    </main>
+  );
+}

app/billing/page.tsx

@@ -0,0 +1,10 @@
+import { BillingManager } from "@/components/billing-manager";
+import { hasSuperAdminAccess } from "@/lib/auth/permissions";
+import { requireAppSession } from "@/lib/server/auth/current-user";
+
+export const dynamic = "force-dynamic";
+
+export default async function BillingPage() {
+  const session = await requireAppSession();
+  return <BillingManager isSuperAdmin={hasSuperAdminAccess(session.user)} />;
+}