Add User Pattern Management and API Integration

Commit notes

This commit introduces a new UserPatternHandler for managing user-specific patterns, including routes for creating, retrieving, updating, and deleting user patterns. It also adds a UserPattern model to represent user patterns in the database. On the frontend, a UserPatternManager component is implemented to allow users to save and load their patterns within the Step Sequencer. Additionally, auto-save functionality is integrated to automatically save user patterns while working in the sequencer, enhancing user experience and data persistence.