feat: 日志中心 + GRE协议支持 + 流量监控 + 部署脚本

- 新增日志中心功能 (api/logapi.go + Logs.vue)
- 新增GRE协议服务支持 (service/gre/)
- 新增流量监控组件 (TrafficChart.vue)
- 新增L2TP/IPSec测试用例
- 新增日志轮转服务 (logrotate.go)
- 新增部署脚本 (scripts/install.sh, uninstall.sh, service文件)
- 更新i18n国际化文件
- 优化后端API和前端路由

frontend/src/locales/zh-CN.json

@@ -207,7 +207,9 @@
     "taskComplete": "全部完成",
     "taskPartialFail": "部分失败",
     "viewTasks": "查看任务",
-    "noTasks": "暂无任务记录"
+    "noTasks": "暂无任务记录",
+    "trafficTrend": "流量趋势",
+    "noTrafficData": "暂无流量数据（等待采样中…）"
   },
   "tunnelEditor": {
     "title": "编辑专线",
@@ -423,6 +425,29 @@
     "kickConfirm": "确定踢用户「{username}」下线？",
     "kicked": "已踢下线"
   },
+  "logs": {
+    "auditTitle": "操作审计日志",
+    "connTitle": "连接审计日志",
+    "alertTitle": "流量告警",
+    "statsTitle": "日志统计",
+    "keywordPlaceholder": "搜索目标/详情",
+    "startDate": "开始日期",
+    "endDate": "结束日期",
+    "exportCsv": "导出 CSV",
+    "eventType": "事件类型",
+    "tunnelId": "隧道ID",
+    "auditCount": "审计日志",
+    "connCount": "连接日志",
+    "sessionCount": "会话记录",
+    "from": "从",
+    "cleanup": "清理日志",
+    "cleanupHint": "删除指定天数之前的日志数据",
+    "cleanupPrompt": "保留最近多少天的日志？",
+    "cleanupInputError": "请输入正整数",
+    "cleanupDone": "清理完成：审计 {audit} 条、连接 {conn} 条、会话 {session} 条",
+    "loadFailed": "加载日志失败",
+    "noAlerts": "暂无流量告警"
+  },
   "settings": {
     "mustChangePassword": "首次登录或密码已被管理员重置，必须修改密码后才能使用其他功能",
     "changePassword": "修改密码",
@@ -451,6 +476,7 @@
     "prodSuggestion": "生产建议",
     "prodSuggestionDesc": "经 Nginx/Caddy 反向代理终止 TLS 后暴露",
     "auditTitle": "操作审计（最近 100 条）",
+    "auditMigrated": "审计日志已迁移至「日志中心」，支持分页、筛选和导出",
     "noAuditLogs": "暂无审计日志",
     "mfaEnabledTitle": "MFA 已启用 — 请保存备用码",
     "backupCodesHint": "这些备用码仅显示一次，丢失手机时用于登录。请立即复制保存！",
@@ -599,6 +625,7 @@
     "vpnUsers": "VPN 拨号用户",
     "plugins": "协议插件",
     "settings": "系统设置",
+    "logs": "日志中心",
     "notFound": "页面不存在",
     "sidebarOps": "专线运维",
     "sidebarResource": "资源管理",