feat(i18n): 添加邮件模板编辑器文案

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/i18n/locales/en.ts

@@ -5805,6 +5805,36 @@ export default {
         sending: 'Sending...',
         enterRecipientHint: 'Please enter a recipient email address'
       },
+      emailTemplates: {
+        title: 'Email Templates',
+        description: 'Customize notification email subjects and HTML content for each event and locale.',
+        event: 'Event',
+        locale: 'Locale',
+        localeEn: 'English',
+        localeZh: 'Chinese',
+        subject: 'Subject',
+        subjectPlaceholder: 'Enter the email subject',
+        html: 'HTML Template',
+        htmlPlaceholder: 'Edit the email HTML template',
+        placeholders: 'Available Placeholders',
+        placeholdersHelp: 'Click a placeholder to copy it. The backend replaces these values when sending emails.',
+        livePreview: 'Live Preview',
+        previewSecurityHint: 'Preview HTML is generated by the backend preview endpoint and displayed in a sandboxed iframe with scripts disabled.',
+        preview: 'Preview / Refresh',
+        previewing: 'Previewing...',
+        save: 'Save Template',
+        saving: 'Saving...',
+        restoreOfficial: 'Restore Official',
+        restoring: 'Restoring...',
+        restoreConfirm: 'Restore the official template for this event and locale? Your custom version will be replaced.',
+        restoreSuccess: 'Official template restored',
+        saveSuccess: 'Email template saved',
+        placeholderCopied: 'Placeholder copied',
+        validationRequired: 'Subject and HTML template are required',
+        empty: 'No email template events or locales are available yet.',
+        noPreview: 'Refresh the preview to see the rendered email subject.',
+        customized: 'Customized'
+      },
       opsMonitoring: {
         title: 'Ops Monitoring',
         description: 'Enable ops monitoring for troubleshooting and health visibility',

frontend/src/i18n/locales/zh.ts

@@ -5965,6 +5965,36 @@ export default {
         sending: '发送中...',
         enterRecipientHint: '请输入收件人邮箱地址'
       },
+      emailTemplates: {
+        title: '邮件模板',
+        description: '按事件和语言自定义通知邮件主题与 HTML 内容。',
+        event: '事件',
+        locale: '语言',
+        localeEn: '英文',
+        localeZh: '中文',
+        subject: '主题',
+        subjectPlaceholder: '输入邮件主题',
+        html: 'HTML 模板',
+        htmlPlaceholder: '编辑邮件 HTML 模板',
+        placeholders: '可用占位符',
+        placeholdersHelp: '点击占位符可复制。后端发送邮件时会替换这些值。',
+        livePreview: '实时预览',
+        previewSecurityHint: '预览 HTML 由后端预览接口生成，并在禁用脚本的沙盒 iframe 中展示。',
+        preview: '预览 / 刷新',
+        previewing: '预览中...',
+        save: '保存模板',
+        saving: '保存中...',
+        restoreOfficial: '恢复官方模板',
+        restoring: '恢复中...',
+        restoreConfirm: '确定恢复此事件和语言的官方模板吗？当前自定义版本将被替换。',
+        restoreSuccess: '已恢复官方模板',
+        saveSuccess: '邮件模板已保存',
+        placeholderCopied: '占位符已复制',
+        validationRequired: '主题和 HTML 模板不能为空',
+        empty: '暂无可用的邮件模板事件或语言。',
+        noPreview: '刷新预览后查看渲染后的邮件主题。',
+        customized: '已自定义'
+      },
       opsMonitoring: {
         title: '运维监控',
         description: '启用运维监控模块，用于排障与健康可视化',