- Add attachment button, file picker, and preview area to ChatInput
- Render image/file attachments in user message bubbles (MessageItem)
- Add Attachment type and attachments field to Message interface
- Add POST /__upload endpoint to both Vite dev server and production server
for saving files to temp directory and returning local file paths
- Translate README to English
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
ekko