Test seamless integration with a2a-samples agents

[tomkis]

Is your feature request related to a problem? Please describe.
We need to validate that plain A2A agents work seamlessly in AgentStack without SDK or modifications.

Describe the solution you'd like
Explore agents from https://github.com/a2aproject/a2a-samples/tree/main/samples/python/agents and test integration:

1. Pick representative agents (e.g. langgraph, crewai, helloworld, ag2)
2. Try adding them via agentstack add <url> or agentstack add <docker-image>
3. Document results:
   • If it works (both CLI + GUI) → record success
   • If it fails → investigate root cause and what AgentStack needs to support it

Additional context
Part of #1918. Ideal outcome: all samples work out of the box.

[tomkis]

When something doesn't work. Make sure a bug / feature is filed and assigned to the #1918

[dosubot]

Hi, @tomkis. I'm Dosu, and I'm helping the agentstack team manage their backlog and am marking this issue as stale.

Issue Summary:

• You requested testing of plain A2A agents from the a2a-samples repo integrated into AgentStack without SDK or modifications.
• The goal is to enable out-of-the-box use via CLI or Docker.
• Documentation of functionality in both CLI and GUI was requested.
• Any bugs or feature requests identified should be filed under issue Epic - Golden path support for plain A2A agents #1918.
• No further updates or activity have been recorded on this issue.

Next Steps:

• Please let us know if this issue is still relevant with the latest version of AgentStack by commenting here.
• If we do not hear back within 7 days, this issue will be automatically closed.

Thank you for your understanding and contribution!