List A2A Agents

List the caller's own A2A-published agent flows, each with its agent-card URL.

Authenticated and owner-scoped, mirroring the MCP-projects catalog: a public cross-user directory would strip the per-flow card's unguessable-id obscurity and expose other users' agents, so this enumerates only the calling user's agents. Each cardUrl is the public discovery entry point an orchestrator fetches per agent.