Add notification scheduling service and integrate settings toggles

[ThalesMMS]

Summary

• add a NotificationScheduler that encapsulates UNUserNotificationCenter scheduling for analysis, urgent, and reminder notifications
• register the scheduler in the dependency container and use it inside NotificationSettingsView, updating feedback copy and reacting to toggle changes
• extract ReminderFrequency into a shared model and cover the scheduler with unit tests using a fake notification center

Testing

• not run (requires Xcode build environment)

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https://chatgpt.com/codex/tasks/task_e_68d1805bb4c4832e9e248aaf6b2697db