Summary

• add Feishu reaction send support via POST /open-apis/im/v1/messages/{message_id}/reactions
• detect single-token emoji-like model output and map to Feishu emoji_type
• fallback to normal text reply when reaction mapping/sending is unavailable
• add unit tests for reaction token detection and emoji mapping
• includes unrelated src/mcp.rs formatting-only changes from cargo fmt

Closes #198