Fix 25 audit issues: memory leaks, concurrency, performance, accessibility

Address findings from comprehensive audit across 5 workstreams:

- Memory: Token-based DataController listeners (prevent closure leaks),
  static DateFormatters, ImageCache observer cleanup, MotionManager
  reference counting, FoundationModels dedup guard
- Concurrency: Replace Task.detached with Task in FeelsApp (preserve
  MainActor isolation), wrap WatchConnectivity handler in MainActor
- Performance: Cache sortedGroupedData in DayViewViewModel, cache demo
  data in MonthView/YearView, remove broken ReduceMotionModifier
- Accessibility: VoiceOver support for LockScreen, DemoHeatmapCell
  labels, MonthCard button labels, InsightsView header traits,
  Smart Invert protection on neon headers

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Shared/Views/SettingsView/SettingsView.swift

@@ -155,11 +155,15 @@ struct SettingsContentView: View {
         .cornerRadius(Constants.viewsCornerRaidus, corners: [.topLeft, .topRight, .bottomLeft, .bottomRight])
     }
 
-    private var formattedReminderTime: String {
-        let onboardingData = UserDefaultsStore.getOnboarding()
+    private static let timeFormatter: DateFormatter = {
         let formatter = DateFormatter()
         formatter.timeStyle = .short
-        return formatter.string(from: onboardingData.date)
+        return formatter
+    }()
+
+    private var formattedReminderTime: String {
+        let onboardingData = UserDefaultsStore.getOnboarding()
+        return Self.timeFormatter.string(from: onboardingData.date)
     }
 
     // MARK: - Section Headers