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/InsightsView/InsightsViewModel.swift

@@ -49,14 +49,24 @@ class InsightsViewModel: ObservableObject {
 
     // MARK: - Initialization
 
+    private var dataListenerToken: DataController.DataListenerToken?
+
     init() {
         isAIAvailable = insightService.isAvailable
 
-        DataController.shared.addNewDataListener { [weak self] in
+        dataListenerToken = DataController.shared.addNewDataListener { [weak self] in
             self?.onDataChanged()
         }
     }
 
+    deinit {
+        if let token = dataListenerToken {
+            Task { @MainActor in
+                DataController.shared.removeDataListener(token: token)
+            }
+        }
+    }
+
     /// Called when mood data changes in another tab. Invalidates cached insights
     /// so they are regenerated with fresh data on next view appearance.
     private func onDataChanged() {