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/en-US.json

@@ -207,7 +207,9 @@
     "taskComplete": "All done",
     "taskPartialFail": "Partial failure",
     "viewTasks": "View Tasks",
-    "noTasks": "No task history"
+    "noTasks": "No task history",
+    "trafficTrend": "Traffic Trend",
+    "noTrafficData": "No traffic data yet (waiting for samples…)"
   },
   "tunnelEditor": {
     "title": "Edit Tunnel",
@@ -423,6 +425,29 @@
     "kickConfirm": "Kick user \"{username}\" offline?",
     "kicked": "User kicked offline"
   },
+  "logs": {
+    "auditTitle": "Audit Logs",
+    "connTitle": "Connection Logs",
+    "alertTitle": "Traffic Alerts",
+    "statsTitle": "Log Statistics",
+    "keywordPlaceholder": "Search target/detail",
+    "startDate": "Start Date",
+    "endDate": "End Date",
+    "exportCsv": "Export CSV",
+    "eventType": "Event Type",
+    "tunnelId": "Tunnel ID",
+    "auditCount": "Audit Logs",
+    "connCount": "Connection Logs",
+    "sessionCount": "Sessions",
+    "from": "From",
+    "cleanup": "Cleanup Logs",
+    "cleanupHint": "Delete log data older than specified days",
+    "cleanupPrompt": "Keep logs from the last how many days?",
+    "cleanupInputError": "Please enter a positive integer",
+    "cleanupDone": "Cleanup done: {audit} audit, {conn} connection, {session} session records deleted",
+    "loadFailed": "Failed to load logs",
+    "noAlerts": "No traffic alerts"
+  },
   "settings": {
     "mustChangePassword": "First login or password has been reset by admin. You must change your password before using other features.",
     "changePassword": "Change Password",
@@ -451,6 +476,7 @@
     "prodSuggestion": "Production Tip",
     "prodSuggestionDesc": "Expose via Nginx/Caddy reverse proxy with TLS termination",
     "auditTitle": "Audit Log (Latest 100)",
+    "auditMigrated": "Audit logs have been moved to Log Center with pagination, filtering, and CSV export",
     "noAuditLogs": "No audit logs yet",
     "mfaEnabledTitle": "MFA Enabled — Please Save Backup Codes",
     "backupCodesHint": "These backup codes are shown only once. Use them to log in if you lose your phone. Copy and save them now!",
@@ -599,6 +625,7 @@
     "vpnUsers": "VPN Dial-in Users",
     "plugins": "Protocol Plugins",
     "settings": "Settings",
+    "logs": "Log Center",
     "notFound": "Page Not Found",
     "sidebarOps": "Tunnel Ops",
     "sidebarResource": "Resource Mgmt",