feat: refine proxy export and toolbar layout

frontend/src/i18n/locales/en.ts

@@ -1903,6 +1903,7 @@ export default {
       editProxy: 'Edit Proxy',
       deleteProxy: 'Delete Proxy',
       dataImport: 'Import',
+      dataExportSelected: 'Export Selected',
       dataImportTitle: 'Import Proxies',
       dataImportHint: 'Upload the exported proxy JSON file to import proxies in bulk.',
       dataImportWarning: 'Import will create or reuse proxies, keep their status, and trigger latency checks after completion.',

frontend/src/i18n/locales/zh.ts

@@ -2012,6 +2012,7 @@ export default {
       deleteConfirmMessage: "确定要删除代理 '{name}' 吗？",
       testProxy: '测试代理',
       dataImport: '导入',
+      dataExportSelected: '导出选中',
       dataImportTitle: '导入代理',
       dataImportHint: '上传代理导出的 JSON 文件以批量导入代理。',
       dataImportWarning: '导入将创建或复用代理，保留状态并在完成后自动触发延迟检测。',