[ML 0.1/UI.03] - User Customization Integration

🎯 The objective

Connect the new Message Item UI to existing user preferences. This ensures the new design respects legacy customization options (density, colours, layouts).

[!NOTE]
This milestone might already be implemented once the others are done. Keeping this milestone for tracking regressions and feedback after the new UI lands to the user.

🎒 Resources

ℹ️ List all relevant resources like BugZilla meta bugs, Figma files, Notion links and other files. These can be filled in later.

🦮 Rules of the Road

🟢 In Scope

• Enable MessageItem to change its spacing by user configuration
• Enable MessageItem to change its number of preview lines by user configuration
• Enable MessageItem background colour change only by user configuration
• Enable Subject and Sender swap in MessageItem UI component
• Hide Favourite button via user's settings

🔴 Out of Scope

• Logic changes to the backend/database (visual only)
• New preference creation (link to existing only)

🚧 Technical and/or Business Requirements

• Spacing: Link the existing user preference for list spacing to the new UI component.
• Preview Lines: Link the existing user preference for line count to the UI.
• Background Colour: Ensure background color changes based on read status only if the user preference ("Change colour when read") is enabled.
• Subject/Sender Swap: Link the existing preference to swap these fields in the layout.
• Hide Favourite: Respect the preference to hide the star/favorite button.