Creates a new agent and allocates cash from your Alpaca account balance.
The cash is reserved for this agent and cannot be double-allocated.

Rules

• name must be lowercase with no spaces (e.g. momentum-trader).
• cash_allocation must be positive and cannot exceed your unallocated
  cash balance.
• Agent names must be unique within your account.

Use case

Create an agent for each distinct strategy you want to run. Each agent
manages its own book independently.

curl -X POST https://api.usetradecraft.io/v1/agents \
  -H "Authorization: Bearer al_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "momentum-trader",
    "cash_allocation": 5000
  }'