feat(admin-v2): add billing management page

- Plan cards with feature comparison and pricing
- Usage progress bars with quota visualization
- Alipay/WeChat Pay method selection modal
- Payment status polling with auto-refresh on success
- Navigation + route registration

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

admin-v2/src/services/billing.ts

@@ -0,0 +1,101 @@
+import request, { withSignal } from './request'
+
+// === Types ===
+
+export interface BillingPlan {
+  id: string
+  name: string
+  display_name: string
+  description: string | null
+  price_cents: number
+  currency: string
+  interval: string
+  features: Record<string, unknown>
+  limits: Record<string, unknown>
+  is_default: boolean
+  sort_order: number
+  status: string
+  created_at: string
+  updated_at: string
+}
+
+export interface Subscription {
+  id: string
+  account_id: string
+  plan_id: string
+  status: string
+  current_period_start: string
+  current_period_end: string
+  trial_end: string | null
+  canceled_at: string | null
+  cancel_at_period_end: boolean
+  created_at: string
+  updated_at: string
+}
+
+export interface UsageQuota {
+  id: string
+  account_id: string
+  period_start: string
+  period_end: string
+  input_tokens: number
+  output_tokens: number
+  relay_requests: number
+  hand_executions: number
+  pipeline_runs: number
+  max_input_tokens: number | null
+  max_output_tokens: number | null
+  max_relay_requests: number | null
+  max_hand_executions: number | null
+  max_pipeline_runs: number | null
+  created_at: string
+  updated_at: string
+}
+
+export interface SubscriptionInfo {
+  plan: BillingPlan
+  subscription: Subscription | null
+  usage: UsageQuota
+}
+
+export interface PaymentResult {
+  payment_id: string
+  trade_no: string
+  pay_url: string
+  amount_cents: number
+}
+
+export interface PaymentStatus {
+  id: string
+  method: string
+  amount_cents: number
+  currency: string
+  status: string
+}
+
+// === Service ===
+
+export const billingService = {
+  listPlans: (signal?: AbortSignal) =>
+    request.get<BillingPlan[]>('/billing/plans', withSignal({}, signal))
+      .then((r) => r.data),
+
+  getPlan: (id: string, signal?: AbortSignal) =>
+    request.get<BillingPlan>(`/billing/plans/${id}`, withSignal({}, signal))
+      .then((r) => r.data),
+
+  getSubscription: (signal?: AbortSignal) =>
+    request.get<SubscriptionInfo>('/billing/subscription', withSignal({}, signal))
+      .then((r) => r.data),
+
+  getUsage: (signal?: AbortSignal) =>
+    request.get<UsageQuota>('/billing/usage', withSignal({}, signal))
+      .then((r) => r.data),
+
+  createPayment: (data: { plan_id: string; payment_method: 'alipay' | 'wechat' }) =>
+    request.post<PaymentResult>('/billing/payments', data).then((r) => r.data),
+
+  getPaymentStatus: (id: string, signal?: AbortSignal) =>
+    request.get<PaymentStatus>(`/billing/payments/${id}`, withSignal({}, signal))
+      .then((r) => r.data),
+}