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/package-lock.json

@@ -14,6 +14,7 @@
         "element-plus": "^2.8.6",
         "qrcode": "^1.5.4",
         "vue": "^3.5.12",
+        "vue-i18n": "^9.14.5",
         "vue-router": "^4.4.5"
       },
       "devDependencies": {
@@ -501,6 +502,50 @@
       "integrity": "sha512-HpCo8tmWzLVad5s2d19EhAz5zqrrQ6s69qd6moPMQvkOuSwDT1YgRfWSVuc4ennqrgv3OHppiOGMQ7oC13yIww==",
       "license": "MIT"
     },
+    "node_modules/@intlify/core-base": {
+      "version": "9.14.5",
+      "resolved": "https://registry.npmjs.org/@intlify/core-base/-/core-base-9.14.5.tgz",
+      "integrity": "sha512-5ah5FqZG4pOoHjkvs8mjtv+gPKYU0zCISaYNjBNNqYiaITxW8ZtVih3GS/oTOqN8d9/mDLyrjD46GBApNxmlsA==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/message-compiler": "9.14.5",
+        "@intlify/shared": "9.14.5"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/message-compiler": {
+      "version": "9.14.5",
+      "resolved": "https://registry.npmjs.org/@intlify/message-compiler/-/message-compiler-9.14.5.tgz",
+      "integrity": "sha512-IHzgEu61/YIpQV5Pc3aRWScDcnFKWvQA9kigcINcCBXN8mbW+vk9SK+lDxA6STzKQsVJxUPg9ACC52pKKo3SVQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/shared": "9.14.5",
+        "source-map-js": "^1.0.2"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
+    "node_modules/@intlify/shared": {
+      "version": "9.14.5",
+      "resolved": "https://registry.npmjs.org/@intlify/shared/-/shared-9.14.5.tgz",
+      "integrity": "sha512-9gB+E53BYuAEMhbCAxVgG38EZrk59sxBtv3jSizNL2hEWlgjBjAw1AwpLHtNaeda12pe6W20OGEa0TwuMSRbyQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      }
+    },
     "node_modules/@jridgewell/sourcemap-codec": {
       "version": "1.5.5",
       "resolved": "https://registry.npmmirror.com/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz",
@@ -1996,6 +2041,27 @@
       "integrity": "sha512-Skkhw9agYSgsWqv7bxSOGJZa9SaiJbZVGdXuFWnrzKaQYHnw9qbjD630rw6RyMqDbp54nfLCLw5SZA55if7JLg==",
       "license": "MIT"
     },
+    "node_modules/vue-i18n": {
+      "version": "9.14.5",
+      "resolved": "https://registry.npmjs.org/vue-i18n/-/vue-i18n-9.14.5.tgz",
+      "integrity": "sha512-0jQ9Em3ymWngyiIkj0+c/k7WgaPO+TNzjKSNq9BvBQaKJECqn9cd9fL4tkDhB5G1QBskGl9YxxbDAhgbFtpe2g==",
+      "deprecated": "v9 and v10 no longer supported. please migrate to v11. about maintenance status, see https://vue-i18n.intlify.dev/guide/maintenance.html",
+      "license": "MIT",
+      "dependencies": {
+        "@intlify/core-base": "9.14.5",
+        "@intlify/shared": "9.14.5",
+        "@vue/devtools-api": "^6.5.0"
+      },
+      "engines": {
+        "node": ">= 16"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/kazupon"
+      },
+      "peerDependencies": {
+        "vue": "^3.0.0"
+      }
+    },
     "node_modules/vue-router": {
       "version": "4.6.4",
       "resolved": "https://registry.npmmirror.com/vue-router/-/vue-router-4.6.4.tgz",