Document the Signed Order spec and non-trusted matching model

[gustavobftorres]

Parent

LIME-Protocol/lime-onchain#3

What to build

Publish the Signed Order specification and trust model so integrators understand how matching, Collateral, signatures, gas payment, and on-chain validation work.

Acceptance criteria

• Signed Order fields, serialization, signing domain, nonce, expiration, and fill semantics are documented
• Docs explain that matching is not trusted and is verified through on-chain Trade Execution
• Docs explain Collateral pre-deposit and who pays gas
• Docs distinguish Trade Execution from post-Resolution Settlement
• Examples are consistent with the SDK API

Blocked by

• Decide the canonical Signed Order spec and Execution Price rule lime-onchain#4