feat: add command dispatch to edge nodes

[Tonyfudecai]

Description

Implement the reverse channel: cloud -> edge command dispatch.

Requirements

• POST /fleet/command: dispatch command to specific node
• Command types: restart, update_config, execute_skill, firmware_update
• Command queue per node (delivered on next heartbeat)
• Command status tracking (pending/delivered/executed/failed)

Skills

Go or TypeScript, async job processing