Implement SSH Phase 13.1: Enterprise-level security configuration

- Add ssh_security_config.rs module (150 lines)
- Define SshSecurityConfig structure (GatewayPorts, PermitOpen, etc.)
- Implement enterprise_default() and development_default()
- Add validate_tcpip_forward_request() security validation
- Add validate_direct_tcpip_channel() security validation
- Integrate SshSecurityConfig into server.rs
- Add SSH_MSG_GLOBAL_REQUEST handling in service loop
- Initialize PortForwardManager for port forwarding
- Create data/ssh_config.json example file
- Support session counting (increment/decrement)
- All compilation tests passed successfully

markbase-core/src/ssh_server/mod.rs

@@ -14,8 +14,10 @@ pub mod channel;
 pub mod sftp_handler;
 pub mod scp_handler;
 pub mod rsync_handler;
-pub mod port_forward;  // Phase 13: 端口转发模块
+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 use server::SshServer;
 pub use packet::{SshPacket, PacketType};
 pub use version::VersionExchange;
+pub use ssh_security_config::SshSecurityConfig;  // Phase 13.1: 导出安全配置