added automated App Store screenshots via iOS simulators and fastlane deliver

tool/screenshots_ios.sh runs the existing demo-login integration test on
iPhone 6.5" (iPhone 14 Plus) and iPad 13" simulators, stores the canonical PNGs
under materials/screenshots and mirrors alpha-free JPEGs to
ios/fastlane/screenshots for `fastlane upload_screenshots`.

Fixed the demo router answering timetable/custom-events with a week, which
crashed the inline iOS widget refresh after a demo login. The screenshot test
now skips the one-time Talk notification dialog and waits longer for the app
shell on cold simulators.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

lib/api/demo/demo_marianumconnect.dart

@@ -32,6 +32,8 @@ class DemoMarianumConnect {
         return DemoTimetable.timegrid().result.map((e) => e.toJson()).toList();
       case 'timetable/holidays':
         return DemoTimetable.holidays().result.map((e) => e.toJson()).toList();
+      case 'timetable/custom-events':
+        return DemoTimetable.customEvents().toJson();
       case 'holidays':
         return DemoHolidays.upcoming().map((e) => e.toJson()).toList();
       case 'users/search':