fix(frontend): 修复i18n翻译中的Invalid linked format错误

问题：
- admin/settings页面无法访问，报错'Invalid linked format'
- vue-i18n解析器将{'@'}误认为链接格式语法

修复：
- 将zh.ts和en.ts中的{'@'}替换为直接的@字符
- 影响范围：代理配置相关的翻译字符串

frontend/src/i18n/locales/en.ts

@@ -1172,9 +1172,9 @@ export default {
       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",
+        "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",
+        "Supports http, https, socks5 protocols. Format: protocol://[user:pass@]host:port",
       parsedCount: '{count} valid',
       invalidCount: '{count} invalid',
       duplicateCount: '{count} duplicate',