Support Feishu (Lark) as a messaging channel

[boycez]

Summary

Add support for Feishu (Lark) as a messaging channel, alongside the existing WeChat channel, so users can interact with the MicroClaw agent directly from Feishu.

Motivation

Feishu/Lark is a widely used collaboration and messaging platform (especially in enterprise and APAC markets). Supporting it as a channel would extend MicroClaw's reach and provide parity with the WeChat integration, letting users drive the agent from a tool they already use daily.

Proposed Scope

• Implement a Feishu channel plugin following the pattern of the existing openclaw-weixin plugin (channel registration via openclaw.plugin.json, inbound/outbound messaging, media handling, auth/session management).
• Support Feishu bot authentication (App ID / App Secret, event subscription / webhook or long-connection).
• Handle inbound messages (text, and ideally images/files) and outbound replies including media.
• Provide a straightforward setup/login flow and documentation.

Open Questions (design needed)

• Auth model: webhook + event subscription vs. Feishu long-connection (WebSocket) mode.
• Message/media capabilities to support in v1 (text-only vs. rich media).
• Single vs. multi-account support.
• Reuse of the existing channel plugin SDK abstractions.

Out of Scope (initial)

• Feishu-specific interactive cards / advanced app features (can be follow-ups).

Filed as a feature request pending design and triage.