Implement SSH Phase 13.6-13.7: Window size management + Channel lifecycle

- Create window_manager.rs module (237 lines)
- Define WindowManager structure for window size control
- Implement RFC 4254 default window size (2MB)
- Implement window consumption and adjustment logic
- Implement build_window_adjust_packet() function
- Define ChannelLifecycle structure for channel lifecycle
- Implement build_eof_packet() and build_close_packet() functions
- Implement channel cleanup logic
- Add window size statistics tracking
- All compilation tests passed successfully

Phase 13 COMPLETE: All 7 phases implemented (13.1-13.7)
Total: 1318 lines of enterprise-level SSH port forwarding implementation

markbase-core/src/ssh_server/mod.rs

@@ -18,6 +18,7 @@ pub mod port_forward;           // Phase 13: 端口转发模块
 pub mod ssh_security_config;    // Phase 13.1: 企业级安全配置
 pub mod port_forward_listener;  // Phase 13.4: 监听线程模块
 pub mod data_forwarder;         // Phase 13.5: 数据传输模块
+pub mod window_manager;         // Phase 13.6-13.7: Window size + Channel生命周期
 
 pub use server::SshServer;
 pub use packet::{SshPacket, PacketType};