Build versioned FX quote integrity service

[BigDella]

Summary

• Adds typed currency/money primitives, deterministic minor-unit rounding, provider adapter interfaces, and static/mock-friendly FX adapters.
• Adds immutable exchange-rate quote snapshots, quote lifecycle rules, transaction quote linkage fields, and legacy FX transaction check tooling.
• Hardens balance-changing request schemas so client-supplied exchange rates are rejected.

Verification

• npm run test -- tests/lib/fx/quote-service.test.ts
• npm run typecheck

Closes #109