fix: 修复历史记录不保存的问题（final 消息类型被错误覆盖为 partial）

internal/ws/handler.go

@@ -75,7 +75,7 @@ func (h *Handler) handleConn(c *websocket.Conn) {
         accMu.Lock()
         accText += msg.Text
         // Send accumulated preview to phone
-        preview := ServerMsg{Type: MsgPartial, Text: accText}
+        preview := ServerMsg{Type: msg.Type, Text: accText}
         accMu.Unlock()
         if err := c.WriteMessage(websocket.TextMessage, preview.Bytes()); err != nil {
           log.Warn("ws write error", "err", err)