Add `vaultless` field to order input/output spec

[findolor]

Overview

Document the new vaultless field for order inputs/outputs in the YAML spec. This field enables direct wallet-based trading in V6 orderbook.

Parent issue: rainlanguage/rain.orderbook#2402

Spec Changes

Add vaultless field to order input/output configuration:

orders:
  my-order:
    inputs:
      - token: token-a
        vaultless: true  # Funds received go directly to wallet
    outputs:
      - token: token-b
        vault-id: 0x123  # Funds go from vault (existing behavior)

Field Definition

Field	Type	Required	Default	Description
vaultless	boolean	No	false	When true, uses wallet directly instead of vault. Contract uses vault_id = 0 internally.

Validation Rules

Scenario	Result
vaultless: true	Valid - uses wallet directly
vaultless: true + vault-id: X	Error: "Using vault-id is not allowed in vaultless mode"
vault-id: 0	Error: "Invalid vault-id value. For vaultless mode use vaultless: true"
vaultless: false or omitted	Uses vault-id if specified, otherwise generates random

Behavior

• Vaultless inputs: Tokens received are sent directly to the owner's wallet
• Vaultless outputs: Tokens given are pulled directly from the owner's wallet (requires approval)
• Hybrid orders: Each input/output can independently be vaultless or vault-based