feature: Implement /chat/{namespace}/{name}/agent-card for local backend

[esnible]

Feature Description

I want to be able to see agent cards when I use authbridge exec to run A2A agents

Proposed Solution

Implement code to query inbound route for agent card and return it via /chat/{namespace}/{name}/agent-card endpoint.

Want to contribute?

• I would like to work on this issue.

Additional Context

No response