Add spawn_agent and check_agent_status tools

Add two minimal tools for agent orchestration:

spawn_agent

Spawns an agent asynchronously. Returns immediately with run_id.

Input:
{
  "task": "string, required - what the agent should do",
  "workflow": "string, optional - coder|researcher|reviewer, default coder",
  "name": "string, optional - human-readable name"
}

Output:
{
  "run_id": "abc123",
  "name": "foo-impl",
  "status": "running"
}

Implementation: Wraps agentd run internally.

check_agent_status

Non-blocking status check on a spawned agent.

Input:
{
  "run_id": "abc123"
}

Output:
{
  "status": "running|completed|failed",
  "result": "...",  // if completed
  "error": "...",   // if failed  
  "cost_cents": 12.5,
  "duration_secs": 45
}

Implementation: Wraps agentd status --json.

Notes

• These are the minimal primitives for the Foreman workflow (Omni/Agent/Workflows/Foreman.md)
• Composition patterns (waiting, racing, pipelines) are taught via skill, not additional tools
• Add to Omni/Agent/Tools.hs or similar