Create a wallet domain module scaffold for balances, addresses, and future signing workflows

[David-patrick-chuks]

Summary

Create a dedicated wallet domain scaffold so wallet-oriented concerns have a clear architectural home in the backend.

Context

Lily Protocol centers on agent-owned wallets, but the backend currently does not yet expose a dedicated wallet module structure.

Scope

• Add a wallet module scaffold
• Define balance/address-oriented types and service boundaries
• Prepare extension points for future signing and settlement flows
• Keep the implementation structural rather than fully feature-complete

Acceptance Criteria

• A wallet module exists with clear service and contract boundaries
• Wallet concerns are separated cleanly from agent concerns
• The scaffold is ready for future integration with payment and settlement features
• Contributors can extend the module predictably

Out of Scope

• Real signing implementation
• On-chain settlement execution
• Full wallet sync engine

Dependencies

Should align with #9 and #24.
Service-level architecture and API contract workflows will help keep the wallet module coherent.