Updated `Base` import to use centralized `app.core.database.Base` for consistency. Enhanced `TimestampMixin` and `UUIDMixin` with docstrings for clarity. Fixed metadata reference in `guest_gifts` table and added relationships in `email_template`.
Created reusable `Base`, `UUIDMixin`, and `TimestampMixin` in `base.py`. Added a `User` model with attributes, relationships, and database configurations in `user.py` to establish a foundation for user-related features.