feat: define Fleet API protocol specification (OpenAPI)

[Tonyfudecai]

Description

Create the OpenAPI 3.0 specification for the Fleet Manager API 鈥?the core communication protocol between edge agents and the cloud.

Endpoints to define

• POST /fleet/register 鈥?node registration
• POST /fleet/heartbeat 鈥?periodic health check
• POST /fleet/events 鈥?event reporting
• POST /fleet/command 鈥?command dispatch
• GET /fleet/nodes 鈥?list all nodes
• GET /fleet/nodes/{id} 鈥?node details

Skills

OpenAPI/Swagger, REST API design