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/billing/service.rs

@@ -300,6 +300,93 @@ pub async fn increment_dimension_by(
     Ok(())
 }
 
+/// 管理员切换用户订阅计划（仅 super_admin 调用）
+///
+/// 1. 验证目标 plan_id 存在且 active
+/// 2. 取消用户当前 active 订阅
+/// 3. 创建新订阅（status=active, 30 天周期）
+/// 4. 更新当月 usage quota 的 max_* 列
+pub async fn admin_switch_plan(
+    pool: &PgPool,
+    account_id: &str,
+    target_plan_id: &str,
+) -> SaasResult<Subscription> {
+    // 1. 验证目标计划存在且 active
+    let plan = get_plan(pool, target_plan_id).await?
+        .ok_or_else(|| crate::error::SaasError::NotFound("目标计划不存在或已下架".into()))?;
+
+    // 2. 检查是否已订阅该计划
+    if let Some(current_sub) = get_active_subscription(pool, account_id).await? {
+        if current_sub.plan_id == target_plan_id {
+            return Err(crate::error::SaasError::InvalidInput("用户已订阅该计划".into()));
+        }
+    }
+
+    let mut tx = pool.begin().await
+        .map_err(|e| crate::error::SaasError::Internal(format!("开启事务失败: {}", e)))?;
+
+    let now = chrono::Utc::now();
+
+    // 3. 取消当前活跃订阅
+    sqlx::query(
+        "UPDATE billing_subscriptions SET status = 'canceled', canceled_at = $1, updated_at = $1 \
+         WHERE account_id = $2 AND status IN ('trial', 'active', 'past_due')"
+    )
+    .bind(&now)
+    .bind(account_id)
+    .execute(&mut *tx)
+    .await?;
+
+    // 4. 创建新订阅
+    let sub_id = uuid::Uuid::new_v4().to_string();
+    let period_start = now;
+    let period_end = now + chrono::Duration::days(30);
+
+    sqlx::query(
+        "INSERT INTO billing_subscriptions \
+         (id, account_id, plan_id, status, current_period_start, current_period_end, created_at, updated_at) \
+         VALUES ($1, $2, $3, 'active', $4, $5, $6, $6)"
+    )
+    .bind(&sub_id)
+    .bind(account_id)
+    .bind(&target_plan_id)
+    .bind(&period_start)
+    .bind(&period_end)
+    .bind(&now)
+    .execute(&mut *tx)
+    .await?;
+
+    // 5. 同步当月 usage quota 的 max_* 列
+    let limits: PlanLimits = serde_json::from_value(plan.limits.clone())
+        .unwrap_or_else(|_| PlanLimits::free());
+    sqlx::query(
+        "UPDATE billing_usage_quotas SET max_input_tokens=$1, max_output_tokens=$2, \
+         max_relay_requests=$3, max_hand_executions=$4, max_pipeline_runs=$5, updated_at=NOW() \
+         WHERE account_id=$6 AND period_start = DATE_TRUNC('month', NOW())"
+    )
+    .bind(limits.max_input_tokens_monthly)
+    .bind(limits.max_output_tokens_monthly)
+    .bind(limits.max_relay_requests_monthly)
+    .bind(limits.max_hand_executions_monthly)
+    .bind(limits.max_pipeline_runs_monthly)
+    .bind(account_id)
+    .execute(&mut *tx)
+    .await?;
+
+    tx.commit().await
+        .map_err(|e| crate::error::SaasError::Internal(format!("事务提交失败: {}", e)))?;
+
+    // 查询返回新订阅
+    let sub = sqlx::query_as::<_, Subscription>(
+        "SELECT * FROM billing_subscriptions WHERE id = $1"
+    )
+    .bind(&sub_id)
+    .fetch_one(pool)
+    .await?;
+
+    Ok(sub)
+}
+
 /// 检查用量配额
 ///
 /// P1-7 修复: 从当前 Plan 读取限额（而非 stale 的 usage 表冗余列）