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/TunnelEditor.vue

@@ -2,19 +2,19 @@
   <el-card class="page-card" shadow="never" v-loading="loading">
     <template #header>
       <div style="display:flex;justify-content:space-between;align-items:center">
-        <b>编辑专线</b>
-        <el-button @click="router.push('/tunnels')">返回列表</el-button>
+        <b>{{ $t('tunnelEditor.title') }}</b>
+        <el-button @click="router.push('/tunnels')">{{ $t('tunnelEditor.backToList') }}</el-button>
       </div>
     </template>
 
     <el-alert type="info" :closable="false" style="margin-bottom:18px"
-      title="密码、PSK、Token 等敏感字段不会回显；留空表示继续使用原值。" />
+      :title="$t('tunnelEditor.sensitiveFieldHint')" />
 
     <el-form v-if="form" label-width="170px" label-position="left" style="max-width:720px">
-      <el-form-item label="专线名称" required>
+      <el-form-item :label="$t('tunnelEditor.tunnelName')" required>
         <el-input v-model="form.name" />
       </el-form-item>
-      <el-form-item label="协议类型">
+      <el-form-item :label="$t('tunnelEditor.protocolType')">
         <el-tag :color="protocolColor(protocol)" effect="dark" style="border:none">{{ protocolDisplay(protocol) }}</el-tag>
       </el-form-item>
       <el-form-item v-for="field in visibleFields" :key="field.key" :label="field.label" :required="field.required">
@@ -24,18 +24,18 @@
           <el-option v-for="option in field.options" :key="optionValue(option)" :label="optionLabel(option)" :value="optionValue(option)" />
         </el-select>
         <el-input v-else-if="field.type === 'password'" v-model="form.config[field.key]" type="password"
-          show-password :placeholder="field.placeholder || '留空保持原值'" />
+          show-password :placeholder="field.placeholder || $t('tunnelEditor.keepOriginal')" />
         <el-input v-else v-model="form.config[field.key]" :placeholder="field.placeholder || field.default" />
         <div v-if="field.tip" class="field-tip">{{ field.tip }}</div>
       </el-form-item>
-      <el-form-item label="到期时间">
-        <el-date-picker v-model="form.expire_at" type="datetime" clearable placeholder="留空为永久" style="width:100%" />
+      <el-form-item :label="$t('tunnelEditor.expireTime')">
+        <el-date-picker v-model="form.expire_at" type="datetime" clearable :placeholder="$t('tunnelEditor.expirePlaceholder')" style="width:100%" />
       </el-form-item>
-      <el-form-item label="自动启动"><el-switch v-model="form.auto_start" /></el-form-item>
-      <el-form-item label="备注"><el-input v-model="form.remark" type="textarea" :rows="3" /></el-form-item>
+      <el-form-item :label="$t('tunnelEditor.autoStart')"><el-switch v-model="form.auto_start" /></el-form-item>
+      <el-form-item :label="$t('common.remark')"><el-input v-model="form.remark" type="textarea" :rows="3" /></el-form-item>
       <el-form-item>
-        <el-button type="primary" :loading="saving" @click="save">保存配置</el-button>
-        <el-button @click="router.push('/tunnels')">取消</el-button>
+        <el-button type="primary" :loading="saving" @click="save">{{ $t('tunnelEditor.saveConfig') }}</el-button>
+        <el-button @click="router.push('/tunnels')">{{ $t('common.cancel') }}</el-button>
       </el-form-item>
     </el-form>
   </el-card>
@@ -45,9 +45,11 @@
 import { computed, onMounted, ref } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { ElMessage } from 'element-plus'
+import { useI18n } from 'vue-i18n'
 import api from '../api'
 import { CUSTOM_FIELDS, PROTOCOL_META, protocolColor, protocolDisplay, optionValue, optionLabel } from '../protocols'
 
+const { t } = useI18n()
 const route = useRoute()
 const router = useRouter()
 const loading = ref(true)
@@ -84,7 +86,7 @@ async function load() {
       config,
     }
   } catch (error) {
-    ElMessage.error(error.response?.data?.error || '加载专线失败')
+    ElMessage.error(error.response?.data?.error || t('tunnelEditor.loadFailed'))
     router.push('/tunnels')
   } finally {
     loading.value = false
@@ -92,14 +94,14 @@ async function load() {
 }
 
 async function save() {
-  if (!form.value.name) return ElMessage.warning('请填写专线名称')
+  if (!form.value.name) return ElMessage.warning(t('tunnelEditor.fillName'))
   saving.value = true
   try {
     await api.put(`/tunnels/${route.params.id}`, form.value)
-    ElMessage.success('配置已保存')
+    ElMessage.success(t('tunnelEditor.configSaved'))
     router.push('/tunnels')
   } catch (error) {
-    ElMessage.error(error.response?.data?.error || '保存失败')
+    ElMessage.error(error.response?.data?.error || t('common.saveFailed'))
   } finally {
     saving.value = false
   }