fix(saas): WorkerDispatcher registration race — consumer starts after all workers registered

Root cause: start_consumer() was called in new() before any register() calls,
so the consumer's cloned HashMap was always empty. Workers like log_operation
and record_usage were never found, causing "Unknown worker" errors.

- Add WorkerDispatcher::start() method to be called after all register()s
- Update main.rs to call dispatcher.start() after 7 workers registered

crates/zclaw-saas/src/main.rs

@@ -48,6 +48,7 @@ async fn main() -> anyhow::Result<()> {
     dispatcher.register(UpdateLastUsedWorker);
     dispatcher.register(AggregateUsageWorker);
     dispatcher.register(GenerateEmbeddingWorker);
+    dispatcher.start(); // 必须在所有 register() 之后调用
     info!("Worker dispatcher initialized (7 workers registered)");
 
     // 优雅停机令牌 — 取消后所有 SSE 流和长连接立即终止

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

@@ -104,8 +104,9 @@ impl WorkerDispatcher {
             spawn_limiter,
         };
 
-        // 启动消费循环
-        dispatcher.start_consumer(receiver);
+        // 注意：不在此处启动消费循环 — 调用方需在 register() 全部完成后调用 start()
+        // 否则 consumer 持有的是空 handlers 克隆
+        let _ = receiver; // 由 start() 消费
 
         dispatcher
     }
@@ -121,6 +122,14 @@ impl WorkerDispatcher {
         );
     }
 
+    /// 启动消费循环（必须在所有 register() 完成后调用）
+    pub fn start(self: &mut Self) {
+        // 重新创建 channel，start_consumer 需要持有最新的 handlers
+        let (sender, receiver) = mpsc::channel(1024);
+        self.sender = sender;
+        self.start_consumer(receiver);
+    }
+
     /// 派发任务（非阻塞）
     pub async fn dispatch<A>(&self, worker_name: &str, args: A) -> SaasResult<()>
     where