feat(ui): 设置页支持启用/禁用 TUN 并改进默认字体回退

- 设置页新增「启用虚拟网卡 (TUN)」复选框；未启用时隐藏虚拟网卡名称输入框，
  显示橙色警告"⚠️ TUNTAP 未启用：虚拟网卡未挂载"，保存时写入 TUNName=null
- 勾选后恢复名称输入框，留空自动填入默认值 KLALB_SRv6
- 控制台同步输出英文警告：禁用时 "WARNING: TUNTAP is disabled..."、
  挂载失败时 "WARNING: Failed to mount TUN adapter..."
- UIEnv 默认字体改为按平台探测回退：
  雅黑/PingFang/Noto 等候选 → 系统 Label.font → Java Dialog 逻辑字体

src/klalb_en_US.properties

@@ -92,6 +92,8 @@ transmitnagledelaytime=Transmit nagle delay time
 linknagledelaytime=Link nagle delay time
 linkconnectionscount=Link connections count
 tunname=Virtual network device name
+enabletun=Enable TUN device
+tundisabledwarning=⚠️ TUNTAP is disabled: Virtual network device not mounted
 dashboard=Dashboard
 backplanedelay=Backplane delay
 backplanepps=Backplane PPS

src/klalb_zh_CN.properties

@@ -92,6 +92,8 @@ transmitnagledelaytime=传输粘包等待时间
 linknagledelaytime=链路粘包等待时间
 linkconnectionscount=链路连接数
 tunname=虚拟网卡名称
+enabletun=启用虚拟网卡 (TUN)
+tundisabledwarning=⚠️ TUNTAP 未启用：虚拟网卡未挂载
 dashboard=仪表盘
 backplanedelay=背板处理延迟
 backplanepps=背板包转发率

src/org/kne/cloud/network/klalb/KLALBController.java

@@ -661,12 +661,13 @@ public class KLALBController {
 				
 			} catch (Exception e) {
 				System.err.println("挂载虚拟网卡失败，可能是无管理员权限？请尝试使用管理员权限运行软件");
+				System.err.println("WARNING: Failed to mount TUN adapter (requires administrator privileges)");
 				e.printStackTrace();
 			}
 			});
 			t.start();
 		}else {
-			System.out.println("    Tun Adapter Disabled");
+			System.out.println("  WARNING: TUNTAP is disabled: Virtual network device not mounted");
 			
 		}
 		udpr=new UDPProtocolRegister(this);

src/org/kne/cloud/network/klalb/ui/KLALBStateGUI3.java

@@ -98,6 +98,9 @@ public class KLALBStateGUI3 extends XFrame {
 	private JCheckBox denyQuery;
     private ClosableTabbedPane tabbedPane;             // 可关闭的标签页面板
 	private JCheckBox nogui;
+	private JCheckBox enableTun;
+	private TextSettingItem tunNameItem;
+	private SettingItem tunWarningItem;
 
     // ==================== 配置和回调 ====================
     private KLALBConfig config;                         // 配置文件
@@ -820,10 +823,29 @@ public class KLALBStateGUI3 extends XFrame {
         asnFieldSet = asn.getTextField();
         settings.getView().add(asn);
         
-        TextSettingItem tunName = new TextSettingItem(UIEnv.getRsb().getString("tunname"), 
+        // 启用虚拟网卡 (TUN)
+        CheckBoxSettingItem enableTunc = new CheckBoxSettingItem(UIEnv.getRsb().getString("enabletun"), 
             CONST.itemwidth, CONST.settingheight);
-        tunDeviceName = tunName.getTextField();
+        enableTun = enableTunc.getCheckBox();
-            settings.getView().add(tunName);
+        settings.getView().add(enableTunc);
+        
+        tunNameItem = new TextSettingItem(UIEnv.getRsb().getString("tunname"), 
+                CONST.itemwidth, CONST.settingheight);
+        tunDeviceName = tunNameItem.getTextField();
+        settings.getView().add(tunNameItem);
+
+        tunWarningItem = new SettingItem(UIEnv.getRsb().getString("tundisabledwarning"), 
+                UIEnv.getFont().deriveFont(13.0f), CONST.itemwidth, CONST.settingheight);
+        tunWarningItem.getLabel().setForeground(new Color(220, 80, 0));
+        settings.getView().add(tunWarningItem);
+
+        enableTun.addActionListener(e -> {
+            boolean en = enableTun.isSelected();
+            if (en && (tunDeviceName.getText().trim().isEmpty() || tunDeviceName.getText().trim().equalsIgnoreCase("null"))) {
+                tunDeviceName.setText(CONST.KLALB_S_RV6);
+            }
+            updateTunVisibility(en);
+        });
         
         // 链接设置标题
         SettingItem six = new SettingItem(UIEnv.getRsb().getString("linksettings"), 
@@ -1026,6 +1048,19 @@ public class KLALBStateGUI3 extends XFrame {
         delayLbound.getSlider().addChangeListener(cll);
     }
 
+    private void updateTunVisibility(boolean enabled) {
+        if (tunNameItem != null) {
+            tunNameItem.setVisible(enabled);
+        }
+        if (tunWarningItem != null) {
+            tunWarningItem.setVisible(!enabled);
+        }
+        if (yspc != null && yspc.getView() != null) {
+            yspc.getView().revalidate();
+            yspc.getView().repaint();
+        }
+    }
+
     // ==================== 配置保存方法 ====================
     /**
      * 保存配置到文件
@@ -1134,12 +1169,17 @@ public class KLALBStateGUI3 extends XFrame {
                     }
                 }
                 
-                String tunNameText=tunDeviceName.getText().trim();
+                // 保存TUN虚拟网卡设置
-                if(tunNameText.equals("") || tunNameText.equalsIgnoreCase("null")) {
+                if (!enableTun.isSelected()) {
                     kck.setTUNName(null);
-                }else {
+                } else {
+                    String tunNameText = tunDeviceName.getText().trim();
+                    if (tunNameText.equals("") || tunNameText.equalsIgnoreCase("null")) {
+                        kck.setTUNName(CONST.KLALB_S_RV6);
+                    } else {
                         kck.setTUNName(tunNameText);
                     }
+                }
                 
                 // 保存TCP监听设置
                 String tcptext = tcpListeningSet.getText();
@@ -1539,7 +1579,10 @@ public class KLALBStateGUI3 extends XFrame {
                 asnFieldSet.setText(vasn != null ? vasn.toString() : "");
                 
                 String tunname=kck.getTUNName();
-                tunDeviceName.setText(tunname!=null?tunname:"");
+                boolean isTunActive = (tunname != null && !tunname.trim().isEmpty() && !tunname.trim().equalsIgnoreCase("null"));
+                enableTun.setSelected(isTunActive);
+                tunDeviceName.setText(isTunActive ? tunname.trim() : "");
+                updateTunVisibility(isTunActive);
                 
                 // 加载TCP监听
                 MultiProtocolSocketAddress mpat = kck.getTCPListen();

src/org/kne/cloud/network/klalb/ui/UIEnv.java

@@ -80,7 +80,7 @@ public class UIEnv {
 				// TODO 自动生成的 catch 块
 				e.printStackTrace();
 			}*/
-			font=new Font("微软雅黑",Font.PLAIN , 12);
+			font = pickDefaultFont(12);
 			/*try {
 				font = Font.createFont(Font.PLAIN, UIEnv.class.getResourceAsStream("/assets/SourceHanSansCN-Light.otf")).deriveFont(13f);
 			} catch (FontFormatException e1) {
@@ -117,6 +117,31 @@ public class UIEnv {
 			start.setFont(font.deriveFont(Font.BOLD, fontsize));
 			start.setBackground(defaultcolor);
 		}
+		private static Font pickDefaultFont(int size) {
+		String[] preferredFonts = new String[] {
+			"Microsoft YaHei UI", "Microsoft YaHei", "微软雅黑",
+			"PingFang SC", ".AppleSystemUIFont", "Helvetica Neue",
+			"Noto Sans CJK SC", "Source Han Sans SC", "WenQuanYi Micro Hei",
+			"Segoe UI", "Arial"
+		};
+		try {
+			String[] available = java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames();
+			java.util.Set<String> set = new java.util.HashSet<>(java.util.Arrays.asList(available));
+			for (String name : preferredFonts) {
+				if (set.contains(name)) {
+					return new Font(name, Font.PLAIN, size);
+				}
+			}
+		} catch (Throwable t) {
+			// fallback in case of headless or security restrictions
+		}
+		Font sysFont = UIManager.getFont("Label.font");
+		if (sysFont != null) {
+			return sysFont.deriveFont(Font.PLAIN, (float) size);
+		}
+		return new Font(Font.DIALOG, Font.PLAIN, size);
+	}
+
 	public static Font getFont(){
 			if(icon==null)
 				inituie();