Optimize app performance, iOS setup

[aikenahac]

Optimized app & animation performance by:

• Creating GoRouter once in initState instead of rebuilding it on every app build.
• Moving SystemChrome.setPreferredOrientations to main() so it runs once.
• Replacing async restore redirects with explicit /restore navigation when shared files are received.
• Switching main tabs to IndexedStack so tab pages stay mounted and avoid full rebuilds during tab changes.
• Adding stable page/storage keys for main tabs and the home scroll view.
• Adding a RepaintBoundary around the home calendar.
• Precomputing calendar day lookup maps in HomePage so calendar builders no longer scan all periods for every visible day.
• Updating PeriodProvider read methods to sort copied lists instead of mutating _periods during builds.
• Removing unused TickerProviderStateMixin from HomePage.
• Updating the widget smoke test to match the real app startup flow.

Note: Requires Android testing, since my testing Android device is not with me at the moment