phase2-03: refactor to oop - transaction engine

[anibalrojosan]

Branch: feat/oop-transaction-engine
Type: backend
Priority: High
Dependencies: phase2-02

Description

Implement a robust transaction engine using OOP principles to handle transfers and deposits between account objects.

Tasks

• Create TransactionManager class in backend/modules/entities.py
• Implement execute_transfer(from_account, to_account, amount) method
• Implement execute_deposit(account, amount) method
• Handle atomic-like operations (ensure both accounts update or none do)
• Integrate transaction recording within the manager

Acceptance Criteria

• Transfers are handled as interactions between Account objects
• Manager correctly handles success/failure states
• Transaction history is updated automatically after execution