Add article export to Word, PDF, and Markdown

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/admin-web/src/i18n/messages/en-US.ts

@@ -1078,6 +1078,22 @@ const enUS = {
     noContent: 'This article does not have generated content yet.',
     editor: {
       publish: 'Publish',
+      download: 'Download',
+      downloadFormats: {
+        word: 'Word',
+        pdf: 'PDF',
+        markdown: 'Markdown',
+      },
+      downloadMessages: {
+        success: 'Download started.',
+        failed: 'Export failed. Please try again.',
+      },
+      markdownExportConfirm: {
+        title: 'Download Markdown',
+        description:
+          'Images will be removed from the Markdown file. Text content such as headings, tables, and links will be kept.',
+        confirm: 'Download',
+      },
       titlePlaceholder: 'Enter article title',
       leaveConfirm: {
         title: 'Unsaved changes',