user_preferences.currency column exists in DB but not in the entity

[RUKAYAT-CODER]

Migration 1710000000000-AddTimezoneLocalePreferences.ts adds currency varchar DEFAULT 'USD' to user_preferences, but UserPreference (src/user-preferences/entities/user-preference.entity.ts) only declares locale, language, timezone, etc. — no currency.

Same consequences as the users/course cases: the column can't be read through the entity and the drift check wants to drop it.

Fix: declare currency on the entity or drop the column.

[Meet-hybrid]

I would like to contribute to this issue. I have experience with JavaScript/TypeScript, React, backend APIs, testing, Git, and software architecture. I will follow the acceptance criteria, add tests, and provide a focused pull request.