Wayfinder: New Position backend implementation slice

[3esmit]

Question

Implement the backend slice required by the decided contract: token holding discovery, pool/config/account queries, PDA derivation, preview data, and submit methods for NewDefinition and AddLiquidity.

Done when QML can call typed async methods and receive deterministic state/error payloads without touching dummy state.

[3esmit]

Implemented in PR #210 by commit 7f88fd0. The backend now uses the stateless Rust amm_client plus fixed C++ wallet orchestration for token discovery, account decoding, PDA derivation, exact quoting, quote hashing, fresh-state revalidation, NewDefinition/AddLiquidity instruction planning, and optimistic external-wallet submission.