fix(frontend): 修复代理快捷添加弹窗的 i18n 解析错误

转义 batchInputPlaceholder 中的 @ 符号，防止 Vue I18n 将其误解析为链接消息语法

frontend/src/i18n/locales/en.ts

@@ -817,7 +817,7 @@ export default {
       standardAdd: 'Standard Add',
       batchAdd: 'Quick Add',
       batchInput: 'Proxy List',
-      batchInputPlaceholder: 'Enter one proxy per line in the following formats:\nsocks5://user:pass@192.168.1.1:1080\nhttp://192.168.1.1:8080\nhttps://user:pass@proxy.example.com:443',
+      batchInputPlaceholder: "Enter one proxy per line in the following formats:\nsocks5://user:pass{'@'}192.168.1.1:1080\nhttp://192.168.1.1:8080\nhttps://user:pass{'@'}proxy.example.com:443",
       batchInputHint: 'Supports http, https, socks5 protocols. Format: protocol://[user:pass@]host:port',
       parsedCount: '{count} valid',
       invalidCount: '{count} invalid',