[Feature]: Support k8s-sig agent sandbox

[jinjiaKarl]

Feature Description

Add a new sandbox backend based on the Kubernetes SIGs Agent Sandbox client to support running self-hosted sandboxes on Kubernetes clusters.

Proposed API/Interface

If applicable, describe how you envision the API or interface would look:

# Python SDK
# Your proposed API here

// TypeScript SDK
// Your proposed API here

Impact Component/Area

Which part of Acontext would this feature affect?

• Client SDK (Python)
• Client SDK (TypeScript)
• Core Service (Python)
• API Server (Go)
• UI/Dashboard (Next.js)
• CLI Tool
• Documentation
• Other (please specify)

Additional Context

Add any other context, mockups, or examples about the feature request here.