✨ Added markdown and mermaid preview

frontend/src/i18n/locales/en-US.ts

@@ -19,6 +19,8 @@ export default {
     searchLanguage: 'Search language...',
     noLanguageFound: 'No language found',
     formatHint: 'Click Format Block (Ctrl+Shift+F)',
+    previewMarkdown: 'Preview Markdown',
+    closePreview: 'Close Preview',
     // Document selector
     selectDocument: 'Select Document',
     searchOrCreateDocument: 'Search or enter new document name...',

frontend/src/i18n/locales/zh-CN.ts

@@ -19,6 +19,8 @@ export default {
     searchLanguage: '搜索语言...',
     noLanguageFound: '未找到匹配的语言',
     formatHint: '点击格式化区块（Ctrl+Shift+F）',
+    previewMarkdown: '预览 Markdown',
+    closePreview: '关闭预览',
     // 文档选择器
     selectDocument: '选择文档',
     searchOrCreateDocument: '搜索或输入新文档名...',