<Changes>
1. Added State enum with ACTIVE and INACTIVE values in Enums.h.
2. Added state member, getter, and setter in User, Service, InventoryItem, and ComboPackage models.
3. Updated constructors to initialize model objects with ACTIVE state by default.
4. Added state string conversion helper functions in Enums.h.
5. Added default return values in Controller getter methods to complete stub implementations.
6. Added basic menu loop implementation in CustomerMenu and TechnicianMenu for handling user input.
</Changes>
Changes:
- Added stub implementations for Controller.cpp methods
- Fixed const issue in UserInterface methods (run, login, registerCustomer, handleOperation)
- Changed return types to use const pointers for read-only objects
- Updated maps and vectors to return const object pointers
- Fixed some function parameter names and signatures for consistency