feat: Update tta agent CLI to use OpenHands backend

[theinterneti]

Summary

Update ttadev/cli/agent.py and ttadev/cli/agents.py to use OpenHands as the execution backend instead of the custom AgentRegistry + AgentPrimitive system.

Current CLI commands

• tta agent list — Lists registered agents from Python registry
• tta agent run <name> <task> — Executes via AgentPrimitive
• tta agents spawn — Fleet spawning

Target state

• tta agent list — List available .agent.md files + OpenHands presets
• tta agent run <name> <task> — Execute via OpenHandsPrimitive with preset matching
• tta agents spawn — Delegate to MCP fleet tool v2 (feat: Implement MCP fleet tool v2 with OpenHands execution #384)

Discovery approach

Instead of Python registry, discover agents from:

1. .github/agents/*.agent.md — Copilot agent definitions
2. OpenHands presets — Programmatic agent configurations
3. .github/copilot-catalog.yml — Composition metadata

Acceptance criteria

• tta agent list shows .agent.md roster
• tta agent run executes via OpenHands
• Backward-compatible flags for transition period
• Help text updated

Depends on

• chore: Archive ttadev/agents/ concrete agent implementations #381 (archive concrete agents)
• feat: Create OpenHands custom presets for TTA.dev agent types #383 (OpenHands presets)

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. If this issue is still relevant, please comment or update it to keep it open.