feat: Feishu (Lark) bot bridge for Step-Realtime-CLI

[rsagacom]

Feature: Feishu (Lark) bot bridge

Enable voice/text-driven CLI programming directly from Feishu (Lark).

What

A bridge service connecting Feishu bot → Step-Realtime-CLI serve API via HTTP. Supports text and voice messages with session persistence.

Design decisions

• Bridge runs as a separate Node.js process under bridges/feishu/
• Communicates with step serve over HTTP (not file system)
• Two event source modes: forward from existing subscriber, or direct Lark SDK WebSocket
• Voice messages: ASR (StepFun) → text → serve → reply
• Session persistence with LRU eviction
• macOS launchd service for production