v0.4.0

Added

• Attachments in export — Legacy rich attachments (URL unfurls, bot cards) are now included in the export JSON
• Blocks in export — Block Kit payloads are preserved as raw JSON in the blocks field
• Attachment fallback in text output — Text-format display shows [添付: <fallback>]
• docs/EXPORT_FORMAT.md — Shared export schema specification

Fixed

• Bot user_id fallback — Bot messages with empty user field now fall back to bot_id