Initial commit: OpenVPN Manager v1.0

OpenVPN Web management console with multi-instance support, client cert
issuance, traffic/connection auditing, certificate expiry reminders,
auto backup/restore.

Stack:
- Backend: Go 1.21+ (Gin + JWT)
- Frontend: Vue 3 + Element Plus + ECharts + Vite
- Storage: JSON file (db.json) + filesystem (pki/, instances/, clients/, backups/)

Features:
- Multi-instance OpenVPN management (independent port/proto/subnet/PKI)
- One-click client certificate issuance with .ovpn (embedded certs)
- Certificate expiry reminders (30-day threshold)
- Connection log parsing (status-version 3)
- Auto backup/restore (tar.gz)
- Audit log for all write operations
- JWT auth (12h TTL)
- One-line install.sh for Ubuntu/Debian/RHEL/Fedora

frontend/src/views/Logs.vue

@@ -0,0 +1,45 @@
+<template>
+  <div>
+    <h2 style="margin-top:0">连接日志</h2>
+    <div style="margin-bottom:12px">
+      <el-select v-model="instanceId" placeholder="选择实例" clearable @change="load" style="width:240px">
+        <el-option v-for="i in instances" :key="i.id" :value="i.id" :label="i.name" />
+      </el-select>
+    </div>
+    <el-table :data="list" stripe>
+      <el-table-column prop="common_name" label="用户" />
+      <el-table-column prop="real_ip" label="来源 IP" width="160" />
+      <el-table-column prop="vpn_ip" label="VPN IP" width="140" />
+      <el-table-column prop="bytes_in" label="下行" width="100">
+        <template #default="{row}">{{ fmt(row.bytes_in) }}</template>
+      </el-table-column>
+      <el-table-column prop="bytes_out" label="上行" width="100">
+        <template #default="{row}">{{ fmt(row.bytes_out) }}</template>
+      </el-table-column>
+      <el-table-column prop="connected_at" label="开始时间" width="170">
+        <template #default="{row}">{{ row.connected_at?.slice(0,19) }}</template>
+      </el-table-column>
+      <el-table-column prop="disconnected_at" label="结束时间" width="170">
+        <template #default="{row}">{{ row.disconnected_at?.slice(0,19) || '-' }}</template>
+      </el-table-column>
+    </el-table>
+  </div>
+</template>
+<script setup>
+import { onMounted, ref } from 'vue'
+import { Logs, Inst } from '@/api'
+
+const list = ref([])
+const instances = ref([])
+const instanceId = ref('')
+
+async function load() { list.value = await Logs.conns(instanceId.value) }
+function fmt(n) {
+  if (!n) return '0'
+  const u = ['B','KB','MB','GB','TB']; let i=0,v=n
+  while (v>=1024 && i<u.length-1) { v/=1024; i++ }
+  return v.toFixed(1)+' '+u[i]
+}
+
+onMounted(async () => { instances.value = await Inst.list(); load() })
+</script>