Implement SSH X11 forwarding Phase 3: Channel structure

- Add x11_forward_context field to Channel struct
- Initialize x11_forward_context: None in all Channel creations
- Prepare for actual X11 data forwarding

All 182 tests pass.

markbase-core/src/ssh_server/channel.rs

@@ -194,6 +194,7 @@ impl ChannelManager {
             direct_tcpip: None,
             forwarded_tcpip: None,
             auth_agent_socket: None,
+            x11_forward_context: None, // Phase 2: X11 forwarding
         };
 
         self.channels.insert(server_channel, channel);
@@ -275,6 +276,7 @@ impl ChannelManager {
             direct_tcpip: Some(direct_tcpip),
             forwarded_tcpip: None,
             auth_agent_socket: None,
+            x11_forward_context: None, // Phase 2: X11 forwarding
         };
 
         self.channels.insert(server_channel, channel);
@@ -350,9 +352,10 @@ impl ChannelManager {
             scp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.4修复
             scp_state: ScpState::Idle,       // ⭐⭐⭐⭐⭐ Phase 8.3: SCP state machine
             scp_output_file: None,           // Phase 17: SCP file receive
-            direct_tcpip: None,
-            forwarded_tcpip: Some(forwarded_tcpip),
+direct_tcpip: None,
+            forwarded_tcpip: None,
             auth_agent_socket: None,
+            x11_forward_context: None, // Phase 2: X11 forwarding
         };
 
         self.channels.insert(server_channel, channel);
@@ -429,6 +432,7 @@ impl ChannelManager {
             direct_tcpip: None,
             forwarded_tcpip: None,
             auth_agent_socket: None,
+            x11_forward_context: None, // Phase 2: X11 forwarding
         };
         
         self.channels.insert(server_channel, channel);
@@ -2291,6 +2295,8 @@ struct Channel {
     forwarded_tcpip: Option<ForwardedTcpipChannel>, // forwarded-tcpip channel（Local forwarding）
     // SSH Agent forwarding
     auth_agent_socket: Option<String>, // SSH agent socket path (SSH_AUTH_SOCK)
+    // Phase 2: X11 forwarding context
+    x11_forward_context: Option<super::x11_forward::X11ForwardContext>, // X11 forwarding context
 }
 
 /// SSH Channel状态（参考OpenSSH channel.c）