perf: streamline billing panel bootstrap

Remove the redundant billing account read, cache packages for one minute, prefetch the billing chunk, and parallelize independent package reads.

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

frontend/src/components/app-sidebar.tsx

@@ -21,6 +21,8 @@ import type { Ref } from "react";
 import { AppLink } from "@/components/app-link";
 import { newChatHref, persistLoginSessionReturn, sessionHref } from "@/lib/chat-session-url";
 import { prefetchSecondaryPage } from "@/lib/secondary-page-data";
+import { prefetchBillingPanel } from "@/lib/billing-panel-loader";
+import { prefetchPaymentPackages } from "@/lib/payment-packages-cache";
 import {
   Sidebar,
   SidebarContent,
@@ -368,7 +370,12 @@ export function AppSidebar({
                   <Menu.Item className="account-menu-item" onClick={onOpenGeneral}>
                     <Settings aria-hidden="true" /><span>通用设置</span><ChevronRight aria-hidden="true" />
                   </Menu.Item>
-                  <Menu.Item className="account-menu-item" onClick={onOpenBilling}>
+                  <Menu.Item
+                    className="account-menu-item"
+                    onPointerEnter={() => { prefetchBillingPanel(); prefetchPaymentPackages(); }}
+                    onPointerDown={() => { prefetchBillingPanel(); prefetchPaymentPackages(); }}
+                    onClick={onOpenBilling}
+                  >
                     <WalletCards aria-hidden="true" /><span>账户与点数</span><small>{account.credits} 点</small>
                   </Menu.Item>
                   <Menu.Separator className="account-menu-separator" />