fix: 终端 PTY 尺寸同步

前端在 xterm fit/resize 后通过 WebSocket 发送 resize 控制消息，后端收到后调用 ChannelShell.setPtySize 触发远端重绘，修复 less/vim/top 等全屏程序只显示部分区域的问题。

同时补齐控制消息解析与 PTY resize 的单测，并修正失配的 SftpControllerTest 断言。

backend/src/main/java/com/sshmanager/controller/TerminalControlMessage.java

@@ -0,0 +1,53 @@
+package com.sshmanager.controller;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.util.Optional;
+
+public class TerminalControlMessage {
+
+    public static final String CONTROL_PREFIX = "__SSHMANAGER__:";
+
+    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
+
+    private String type;
+    private Integer cols;
+    private Integer rows;
+
+    public String getType() {
+        return type;
+    }
+
+    public void setType(String type) {
+        this.type = type;
+    }
+
+    public Integer getCols() {
+        return cols;
+    }
+
+    public void setCols(Integer cols) {
+        this.cols = cols;
+    }
+
+    public Integer getRows() {
+        return rows;
+    }
+
+    public void setRows(Integer rows) {
+        this.rows = rows;
+    }
+
+    public static Optional<TerminalControlMessage> parse(String payload) {
+        if (payload == null || !payload.startsWith(CONTROL_PREFIX)) {
+            return Optional.empty();
+        }
+
+        String json = payload.substring(CONTROL_PREFIX.length());
+        try {
+            return Optional.of(OBJECT_MAPPER.readValue(json, TerminalControlMessage.class));
+        } catch (Exception e) {
+            return Optional.empty();
+        }
+    }
+}

backend/src/main/java/com/sshmanager/controller/TerminalWebSocketHandler.java

@@ -100,15 +100,26 @@ public class TerminalWebSocketHandler extends TextWebSocketHandler {
         }
     }
 
-    @Override
-    protected void handleTextMessage(WebSocketSession webSocketSession, TextMessage message) throws Exception {
-        SshService.SshSession sshSession = sessions.get(webSocketSession.getId());
-        if (sshSession != null && sshSession.isConnected()) {
-            lastActivity.put(webSocketSession.getId(), System.currentTimeMillis());
-            sshSession.getInputStream().write(message.asBytes());
-            sshSession.getInputStream().flush();
-        }
-    }
+    @Override
+    protected void handleTextMessage(WebSocketSession webSocketSession, TextMessage message) throws Exception {
+        SshService.SshSession sshSession = sessions.get(webSocketSession.getId());
+        if (sshSession != null && sshSession.isConnected()) {
+            lastActivity.put(webSocketSession.getId(), System.currentTimeMillis());
+
+            String payload = message.getPayload();
+            TerminalControlMessage.parse(payload).ifPresent(ctrl -> {
+                if ("resize".equals(ctrl.getType()) && ctrl.getCols() != null && ctrl.getRows() != null) {
+                    sshSession.resize(ctrl.getCols(), ctrl.getRows());
+                }
+            });
+            if (payload != null && payload.startsWith(TerminalControlMessage.CONTROL_PREFIX)) {
+                return;
+            }
+
+            sshSession.getInputStream().write(message.asBytes());
+            sshSession.getInputStream().flush();
+        }
+    }
 
     @Override
     public void afterConnectionClosed(WebSocketSession webSocketSession, CloseStatus status) throws Exception {

backend/src/main/java/com/sshmanager/service/SshService.java

@@ -85,14 +85,27 @@ public class SshService {
             return outputStream;
         }
 
-        public OutputStream getInputStream() {
-            return inputStream;
-        }
+        public OutputStream getInputStream() {
+            return inputStream;
+        }
+
+        public void resize(int cols, int rows) {
+            if (cols <= 0 || rows <= 0) {
+                return;
+            }
+            if (channel == null) {
+                return;
+            }
+            try {
+                channel.setPtySize(cols, rows, 0, 0);
+            } catch (Exception ignored) {
+            }
+        }
 
-        public void disconnect() {
-            if (channel != null && channel.isConnected()) {
-                channel.disconnect();
-            }
+        public void disconnect() {
+            if (channel != null && channel.isConnected()) {
+                channel.disconnect();
+            }
             if (session != null && session.isConnected()) {
                 session.disconnect();
             }