Settings changes stop restarting everything

Opening Settings should not punish me by restarting the whole slideshow. The app now understands the difference between a harmless visit, a playback adjustment, and a filter change that genuinely requires a new rotation.

Changelog

• Leaving Settings without changing anything now continues the current slideshow without restarting it.
• Playback-only adjustments keep the current rotation moving, while changing playback order continues from the photo or video already on screen.
• Source, date-range, and media-type changes still refresh the library so the rotation always matches the selected filters.
• Settings now regains a usable selection after returning to an already-open panel.
• Nested Settings screens keep their place and restore the prior control when possible.
• Improved first-time Photos setup so the default slideshow starts automatically after access is granted.
• Added clear guidance when iCloud Photos still needs to be enabled or is syncing on Apple TV.
• Made Live Photos a child of Photos so they can remain in the slideshow while their motion is turned off.
• Improved the internal Validation screen so its complete diagnostic snapshot can be reached with the Apple TV remote.
• Reduced slideshow startup contention by loading the current item first and preparing only two upcoming items at a time.
• Stopped unfinished skipped items from continuing to use loading resources in the background.
• Made Back history reflect only photos and videos that were actually shown.