fix(admin): 行业选择500修复 + 管理员切换订阅计划

- fix(industry): list_industries SQL参数编号错位 — count查询和items查询
  共用WHERE子句但参数从$3开始，sqlx bind按$1/$2顺序绑定导致500
- feat(billing): 新增 PUT /admin/accounts/:id/subscription 端点 (super_admin)
  验证目标计划 → 取消当前订阅 → 创建新订阅(30天) → 同步配额
- feat(admin-v2): Accounts.tsx 编辑弹窗新增「订阅计划」选择区
  显示所有活跃计划，保存时调用admin switch plan API

admin-v2/src/services/billing.ts

@@ -90,4 +90,9 @@ export const billingService = {
   getPaymentStatus: (id: string, signal?: AbortSignal) =>
     request.get<PaymentStatus>(`/billing/payments/${id}`, withSignal({}, signal))
       .then((r) => r.data),
+
+  /** 管理员切换用户订阅计划 (super_admin only) */
+  adminSwitchPlan: (accountId: string, planId: string) =>
+    request.put<{ success: boolean; subscription: Subscription }>(`/admin/accounts/${accountId}/subscription`, { plan_id: planId })
+      .then((r) => r.data),
 }