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

crates/zclaw-saas/src/main.rs

@@ -359,6 +359,7 @@ async fn build_router(state: AppState) -> axum::Router {
         .merge(zclaw_saas::scheduled_task::routes())
         .merge(zclaw_saas::telemetry::routes())
         .merge(zclaw_saas::billing::routes())
+        .merge(zclaw_saas::billing::admin_routes())
         .merge(zclaw_saas::knowledge::routes())
         .merge(zclaw_saas::industry::routes())
         .layer(middleware::from_fn_with_state(