Add rich calendar layout

[chrisbrummel]

Summary

• Adds an optional Rich Display on Calendar setting in Display preferences.
• Moves Calendar dates into pinned section headers in rich mode and expands rows into the freed space.
• Adds poster artwork to rich Calendar rows while preserving the classic side-date layout when the setting is disabled.
• Updates the Today button behavior so it scrolls to today at the top of the view with an ease-out animation.

Testing

• Built and installed on the iOS 26.5 simulator and iPhone 17.