Summary

This PR replaces the legacy "Force Dark Mode (restart app)" toggle with a proper Appearance picker offering three options: System, Light, and Dark. Changes now apply immediately without requiring an app restart, and the app properly responds to iOS/MacOS system appearance changes when in "System" mode.

Before:

• Toggle: "Force Dark Mode (restart app)"
• Required app restart to take effect
• Only two options: Dark or System default

After:

• Picker with three options: System, Light, Dark
• Changes apply immediately without restart
• Properly follows iOS/MacOS system appearance when in "System" mode
• New installs default to "System"

Test plan

• Fresh install: Verify default is "System" and app follows iOS/MacOS appearance
• Change appearance in Settings → General → Appearance and verify immediate update
• Set to "System" mode, then change iOS Settings → Display & Brightness → verify LoopFollow updates
• Verify all tabs update correctly (Home, Alarms, Remote, Nightscout, More, Settings)
• Verify modal views also update (Settings opened from More menu)
• Test migration: Install previous version with Dark Mode ON, update, verify migrates to "Dark"
• Test migration: Install previous version with Dark Mode OFF, update, verify migrates to "System"

Technical Details

New File: AppearanceMode.swift

New enum providing helpers for both SwiftUI and UIKit:

enum AppearanceMode: String, CaseIterable, Codable {
    case system
    case light
    case dark

    var colorScheme: ColorScheme? {
        switch self {
        case .system: return nil      // SwiftUI follows system
        case .light: return .light
        case .dark: return .dark
        }
    }

    var userInterfaceStyle: UIUserInterfaceStyle {
        switch self {
        case .system: return .unspecified  // UIKit follows system
        case .light: return .light
        case .dark: return .dark
        }
    }
}

Reactive Updates

UIKit view controllers subscribe to appearance changes via Combine for immediate updates without restart.

System Appearance Detection

When in "System" mode, MainViewController detects iOS/MacOS appearance changes via traitCollectionDidChange and broadcasts a notification so all other view controllers update accordingly.

Migration

• forceDarkMode = true → appearanceMode = .dark
• forceDarkMode = false → appearanceMode = .system
• New installs default to .system

Files Changed

SwiftUI Views Updated (16 files)

• AddAlarmSheet.swift
• AlarmEditor.swift
• AlarmListView.swift
• AlarmSettingsView.swift
• AlarmsContainerView.swift
• BackgroundRefreshSettingsView.swift
• SimpleQRCodeScannerView.swift
• InfoDisplaySettingsView.swift
• LogView.swift
• NightscoutSettingsView.swift
• RemoteSettingsView.swift
• AdvancedSettingsView.swift
• CalendarSettingsView.swift
• ContactSettingsView.swift
• DexcomSettingsView.swift
• GraphSettingsView.swift
• TabCustomizationModal.swift

UIKit View Controllers Updated (7 files)

• MainViewController.swift - Central coordinator, updates window-level style
• SettingsViewController.swift
• MoreMenuViewController.swift
• NightscoutViewController.swift
• AlarmViewController.swift
• RemoteViewController.swift
• SnoozerViewController.swift