[MM6] - Get / Transfer Routes

1. Get all transfers affecting Account
2. Get all transfers affecting Budget
3. Get all transfers affecting World Account
4. Transfer Budget A to Budget B (with transfers logged)

Start by locating the existing route entry points and transfer-related models or services for accounts, budgets, and world accounts. Review how current routes record transfers before defining the four requested operations. Done means all listed retrieval and budget-to-budget transfer routes work, with transfers logged where requested.

Written by the indexing model from the issue text.