Emoji, GIF, and file attachments in private messages

Already implemented. The private message composer supports:

• Emoji picker — click the smiley face in the toolbar
• GIF search — click the GIF button in the toolbar (requires GIPHY API key in admin config)
• File attachments — click Attach to send images, PDFs, documents, audio, video, and archives
• Markdown formatting — bold, italic, links, code, lists via the toolbar

All of this is available on the conversation page at /messages/{id}. Access it by clicking Messages in your user menu or the message icon.