Add Feishu (飞书) channel plugin for enterprise messaging in China/International.
Features:
- WebSocket and Webhook connection modes
- DM and group chat support with @mention gating
- Inbound media support (images, files, PDFs)
- Card render mode with syntax highlighting
- Typing indicator via emoji reactions
- Pairing flow for DM approval
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
