fix: 发布前审计 Batch 1 — Pipeline 内存泄漏/超时 + Director 死锁 + Rate Limit Worker

Pipeline executor:
- 添加 cleanup() 方法，MAX_COMPLETED_RUNS=100 上限淘汰旧记录
- 每步执行添加 tokio::time::timeout（使用 PipelineSpec.timeout_secs，默认 300s）
- Delay ms 上限 60000，超出 warn 并截断

Director send_to_agent:
- 重构为 oneshot::channel 响应模式，避免 inbox + pending_requests 锁竞争
- 添加 ensure_inbox_reader() 独立任务分发响应到对应 oneshot sender

cleanup_rate_limit Worker:
- 实现 Worker body: DELETE FROM rate_limit_events WHERE created_at < NOW() - INTERVAL '1 hour'

651 tests passed, 0 failed

crates/zclaw-saas/src/workers/cleanup_rate_limit.rs

@@ -1,4 +1,7 @@
 //! 清理过期 Rate Limit 条目 Worker
+//!
+//! rate_limit_events 表中的持久化条目会无限增长。
+//! 此 Worker 定期删除超过 1 小时的旧条目，防止数据库膨胀。
 
 use async_trait::async_trait;
 use sqlx::PgPool;
@@ -21,10 +24,31 @@ impl Worker for CleanupRateLimitWorker {
         "cleanup_rate_limit"
     }
 
-    async fn perform(&self, _db: &PgPool, _args: Self::Args) -> SaasResult<()> {
-        // Rate limit entries are in-memory (DashMap), not in DB
-        // This worker is a placeholder for when rate limits are persisted
-        // Currently the cleanup happens in main.rs background task
+    async fn perform(&self, db: &PgPool, args: Self::Args) -> SaasResult<()> {
+        let retention_secs = args.window_secs.max(3600); // 至少保留 1 小时
+
+        let result = sqlx::query(
+            "DELETE FROM rate_limit_events WHERE created_at < NOW() - ($1 || ' seconds')::interval"
+        )
+        .bind(retention_secs.to_string())
+        .execute(db)
+        .await;
+
+        match result {
+            Ok(r) => {
+                let deleted = r.rows_affected();
+                if deleted > 0 {
+                    tracing::info!(
+                        "[cleanup_rate_limit] Deleted {} expired rate limit events (retention: {}s)",
+                        deleted, retention_secs
+                    );
+                }
+            }
+            Err(e) => {
+                tracing::error!("[cleanup_rate_limit] Failed to clean up rate limit events: {}", e);
+            }
+        }
+
         Ok(())
     }
 }