feat: 全协议一键安装 + 国内GitHub镜像加速 + 中英文i18n国际化

后端:
- binmgr.go: 新增 detectChina() 国内/海外自动判断（ipinfo.io）
- binmgr.go: 国内自动走 gh-proxy.com 镜像加速 GitHub 下载
- binmgr.go: 新增 InstallViaPackageManager() 包管理器一键安装
- binmgr.go: 新增 GetDeploySpec()/ProtocolAlias() 导出函数
- api.go: installBinary 支持全部7个协议（FRP/WireGuard/OpenVPN/IPSec/IKEv2/L2TP/StrongSwan）
- api.go: 策略: GitHub下载失败 → 自动降级包管理器安装

前端:
- 安装 vue-i18n@9, 支持中英文切换
- 新增 locales/zh-CN.json + en-US.json (548个翻译key, 17个模块)
- 新增 i18n.js 配置, localStorage 持久化语言偏好
- Layout.vue 右上角语言切换下拉菜单
- 所有17个Vue文件中文文本转为 $t() 调用
- Element Plus 组件语言跟随切换
- TunnelWizard: 所有协议显示「一键安装」按钮(带loading)
- 前端构建零错误

frontend/src/views/Sessions.vue

@@ -5,72 +5,72 @@
       <template #header>
         <div class="row-between">
           <div>
-            <b>在线会话</b>
-            <el-tag size="small" type="success" style="margin-left:8px">{{ sessions.length }} 个在线</el-tag>
+            <b>{{ $t('sessions.title') }}</b>
+            <el-tag size="small" type="success" style="margin-left:8px">{{ $t('sessions.onlineCount', { count: sessions.length }) }}</el-tag>
           </div>
-          <el-button link @click="load">刷新</el-button>
+          <el-button link @click="load">{{ $t('common.refresh') }}</el-button>
         </div>
       </template>
       <el-table :data="sessions" size="default" v-loading="loading">
-        <el-table-column prop="username" label="用户名" min-width="120" />
-        <el-table-column label="协议" width="100">
+        <el-table-column prop="username" :label="$t('common.username')" min-width="120" />
+        <el-table-column :label="$t('common.protocol')" width="100">
           <template #default="{ row }">
             <span class="protocol-tag" :style="{ color: protocolColor(row.protocol) }">{{ protocolDisplay(row.protocol) }}</span>
           </template>
         </el-table-column>
-        <el-table-column prop="real_address" label="公网地址" min-width="140" />
-        <el-table-column prop="virtual_address" label="VPN IP" min-width="120" />
-        <el-table-column label="已连接时长" width="120">
+        <el-table-column prop="real_address" :label="$t('sessions.publicAddress')" min-width="140" />
+        <el-table-column prop="virtual_address" :label="$t('sessions.vpnIp')" min-width="120" />
+        <el-table-column :label="$t('sessions.connectedDuration')" width="120">
           <template #default="{ row }">{{ fmtDuration(row.connected_at) }}</template>
         </el-table-column>
-        <el-table-column label="流量 ↓ / ↑" width="140">
+        <el-table-column :label="$t('common.traffic')" width="140">
           <template #default="{ row }">
             <span style="font-size:12px">{{ fmtBytes(row.rx_bytes) }} / {{ fmtBytes(row.tx_bytes) }}</span>
           </template>
         </el-table-column>
-        <el-table-column label="操作" width="100">
+        <el-table-column :label="$t('common.operation')" width="100">
           <template #default="{ row }">
-            <el-button type="danger" size="small" link @click="disconnect(row)">踢下线</el-button>
+            <el-button type="danger" size="small" link @click="disconnect(row)">{{ $t('sessions.kickOffline') }}</el-button>
           </template>
         </el-table-column>
-        <template #empty><el-empty description="当前无在线用户" /></template>
+        <template #empty><el-empty :description="$t('sessions.noOnlineUsers')" /></template>
       </el-table>
     </el-card>
 
     <!-- 异常流量告警 -->
     <el-card class="page-card" shadow="never" style="margin-bottom:16px" v-if="alerts.length">
-      <template #header><b style="color:var(--color-danger)">⚠ 异常流量告警</b></template>
+      <template #header><b style="color:var(--color-danger)">{{ $t('sessions.trafficAlert') }}</b></template>
       <el-table :data="alerts" size="small">
-        <el-table-column prop="created_at" label="时间" width="170">
-          <template #default="{ row }">{{ new Date(row.created_at).toLocaleString('zh-CN') }}</template>
+        <el-table-column prop="created_at" :label="$t('common.time')" width="170">
+          <template #default="{ row }">{{ new Date(row.created_at).toLocaleString() }}</template>
         </el-table-column>
-        <el-table-column prop="username" label="用户/隧道" width="100" />
-        <el-table-column label="类型" width="100">
+        <el-table-column prop="username" :label="$t('sessions.userTunnel')" width="100" />
+        <el-table-column :label="$t('sessions.alertType')" width="100">
           <template #default="{ row }">
             <el-tag :type="row.event === 'rate_alert' ? 'warning' : 'danger'" size="small">
-              {{ { rate_alert: '突发流量', quota_exceed: '配额超额' }[row.event] || row.event }}
+              {{ { rate_alert: $t('sessions.rateAlert'), quota_exceed: $t('sessions.quotaExceed') }[row.event] || row.event }}
             </el-tag>
           </template>
         </el-table-column>
-        <el-table-column prop="detail" label="详情" show-overflow-tooltip />
+        <el-table-column prop="detail" :label="$t('common.detail')" show-overflow-tooltip />
       </el-table>
     </el-card>
 
     <!-- 连接审计日志 -->
     <el-card class="page-card" shadow="never">
-      <template #header><b>连接审计日志</b></template>
+      <template #header><b>{{ $t('sessions.auditLog') }}</b></template>
       <el-table :data="logs" size="small" max-height="500">
-        <el-table-column prop="created_at" label="时间" width="170">
-          <template #default="{ row }">{{ new Date(row.created_at).toLocaleString('zh-CN') }}</template>
+        <el-table-column prop="created_at" :label="$t('common.time')" width="170">
+          <template #default="{ row }">{{ new Date(row.created_at).toLocaleString() }}</template>
         </el-table-column>
-        <el-table-column prop="username" label="用户" width="100" />
-        <el-table-column label="事件" width="100">
+        <el-table-column prop="username" :label="$t('common.username')" width="100" />
+        <el-table-column :label="$t('sessions.event')" width="100">
           <template #default="{ row }">
             <el-tag :type="eventTagType(row.event)" size="small">{{ eventLabel(row.event) }}</el-tag>
           </template>
         </el-table-column>
-        <el-table-column prop="ip_address" label="IP 地址" width="140" />
-        <el-table-column prop="detail" label="详情" show-overflow-tooltip />
+        <el-table-column prop="ip_address" :label="$t('common.ipAddress')" width="140" />
+        <el-table-column prop="detail" :label="$t('common.detail')" show-overflow-tooltip />
       </el-table>
     </el-card>
   </div>
@@ -79,9 +79,11 @@
 <script setup>
 import { ref, onMounted, onUnmounted } from 'vue'
 import { ElMessage, ElMessageBox } from 'element-plus'
+import { useI18n } from 'vue-i18n'
 import api from '../api'
 import { protocolColor, protocolDisplay } from '../protocols'
 
+const { t } = useI18n()
 const sessions = ref([])
 const logs = ref([])
 const alerts = ref([])
@@ -94,15 +96,15 @@ function fmtBytes(n) {
   while (n >= 1024 && i < 4) { n /= 1024; i++ }
   return n.toFixed(1) + ' ' + u[i]
 }
-function fmtDuration(t) {
-  if (!t) return '-'
-  const sec = Math.floor((Date.now() - new Date(t).getTime()) / 1000)
-  if (sec < 60) return `${sec}秒`
-  if (sec < 3600) return `${Math.floor(sec / 60)}分钟`
-  return `${Math.floor(sec / 3600)}小时${Math.floor((sec % 3600) / 60)}分`
+function fmtDuration(dur) {
+  if (!dur) return '-'
+  const sec = Math.floor((Date.now() - new Date(dur).getTime()) / 1000)
+  if (sec < 60) return t('sessions.seconds', { n: sec })
+  if (sec < 3600) return t('sessions.minutes', { n: Math.floor(sec / 60) })
+  return t('sessions.hoursMinutes', { h: Math.floor(sec / 3600), m: Math.floor((sec % 3600) / 60) })
 }
 function eventLabel(e) {
-  return { connect: '连接', disconnect: '断开', auth_fail: '认证失败', quota_exceed: '配额超额', rate_alert: '突发流量' }[e] || e
+  return { connect: t('sessions.eventConnect'), disconnect: t('sessions.eventDisconnect'), auth_fail: t('sessions.eventAuthFail'), quota_exceed: t('sessions.eventQuotaExceed'), rate_alert: t('sessions.eventRateAlert') }[e] || e
 }
 function eventTagType(e) {
   return { connect: 'success', disconnect: 'info', auth_fail: 'danger', quota_exceed: 'warning', rate_alert: 'warning' }[e] || 'info'
@@ -120,17 +122,17 @@ async function load() {
     logs.value = l.data || []
     alerts.value = a.data || []
   } catch (e) {
-    ElMessage.error('加载数据失败')
+    ElMessage.error(t('sessions.loadDataFailed'))
   } finally { loading.value = false }
 }
 
 async function disconnect(row) {
   try {
-    await ElMessageBox.confirm(`确定踢用户「${row.username}」下线？`, '确认', { type: 'warning' })
+    await ElMessageBox.confirm(t('sessions.kickConfirm', { username: row.username }), t('common.confirm'), { type: 'warning' })
     await api.post(`/sessions/${row.id}/disconnect`)
-    ElMessage.success('已踢下线')
+    ElMessage.success(t('sessions.kicked'))
     load()
-  } catch (e) { if (e !== 'cancel') ElMessage.error('操作失败') }
+  } catch (e) { if (e !== 'cancel') ElMessage.error(t('common.operationFailed')) }
 }
 
 let timer