Refactor Command Processing / CQRS Sub-system

Apache Fineract’s current command processing system relies on a centralized service and untyped JSON payloads, which limits type safety and causes errors to surface only at runtime. In a financial system, such issues can disrupt critical operations and reduce reliability. This project proposes to migrate selected modules to the new CQRS-based fineract-command architecture, which introduces typed commands, structured handler dispatch, and extensible processing hooks. The migration will cover the full request lifecycle—from REST APIs to business logic—while strictly preserving backward compatibility through unchanged integration tests. Key deliverables include migrating open and unassigned modules to the new architecture, introducing type-safe DTOs with validation, replacing legacy JAX-RS endpoints with Spring Web MVC controllers, integrating the CommandPipeline with typed handlers, removing obsolete legacy components, and producing a comprehensive migration guide to enable future contributions.