R2: Minimum transaction types

R2.1: The app should track at least 5 types of transactions, including purchases from campus stores, transfers between users, and withdrawals from linked bank accounts.

Look for transaction models or schemas in the codebase to understand the current data structure. Identify where transaction types are defined and how new types can be added. Check for existing API endpoints or services handling purchases, transfers, and withdrawals to see how to extend them. Verify the feature by ensuring at least five distinct transaction types are implemented and testable.

Written by the indexing model from the issue text.