Add shortcuts preferences to User model

[karenrasmussen]

Description

This PR introduces support for user-specific keyboard shortcuts by extending the User model with a new shortcuts_preferences attribute.

The goal is to allow each user to customize and persist their own shortcut configuration.

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Solution

• Added a new shortcuts_preferences attribute to the User model to store shortcut-related preferences.
• Updated the update_preferences method to properly handle and persist shortcut preferences.
• Adjusted the user_preferences logic to include the new shortcuts configuration.