Reposition the backend as a reference Order Book implementation

[gustavobftorres]

Parent

LIME-Protocol/lime-onchain#3

What to build

Make the backend clearly read as a forkable reference implementation for integrators, not as the canonical LIME protocol backend.

Acceptance criteria

• README and API docs describe the backend as a reference Order Book
• Docs state that matching is not trusted and truth is enforced on-chain
• LIME-specific branding is reduced where it gets in the way of reuse
• Setup instructions help integrators fork and adapt the service

Blocked by

• Refactor the reference Order Book to consume Signed Orders #2