fix: 修复raceDial竞态条件导致daemon死锁无法连接

raceDial在首个连接成功后cancel剩余拨号goroutine时，dial goroutine
的select有两个同时就绪的case（缓冲channel可发送 vs raceCtx.Done()），
Go随机选择可能导致结果未发送，使drain循环永久阻塞，进而导致daemon
持有d.mu死锁，所有IPC命令(stats/stop/新start)全部阻塞。

DNS解析返回IPv4+IPv6双地址时触发此bug，约50%概率死锁。

修复：移除select，直接发送到缓冲channel（容量=len(ips)永不阻塞），
多余连接由drain循环负责关闭。

internal/transport/racedial.go

@@ -99,13 +99,13 @@ func raceDial(ctx context.Context, network string, ips []string, port string) (n
 		go func(target string) {
 			d := &net.Dialer{}
 			c, err := d.DialContext(raceCtx, network, net.JoinHostPort(target, port))
-			select {
-			case resultCh <- result{conn: c, err: err}:
-			case <-raceCtx.Done():
-				if c != nil {
-					c.Close()
-				}
-			}
+			// Always send the result: resultCh is buffered (len(ips)),
+			// so this never blocks. Do NOT use a select with
+			// <-raceCtx.Done() here - when the context is cancelled
+			// both cases would be ready and Go's random select pick
+			// could skip the send, causing the drain loop below to
+			// block forever.
+			resultCh <- result{conn: c, err: err}
 		}(ip)
 	}
 
@@ -117,7 +117,8 @@ func raceDial(ctx context.Context, network string, ips []string, port string) (n
 			// any late successful connections.
 			cancel()
 			for j := i + 1; j < len(ips); j++ {
-				if late := <-resultCh; late.conn != nil {
+				late := <-resultCh
+				if late.conn != nil {
 					late.conn.Close()
 				}
 			}