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/FeelsApp.swift

@@ -106,7 +106,7 @@ struct FeelsApp: App {
                 }
 
                 // Defer all non-critical foreground work to avoid blocking UI
-                Task.detached(priority: .utility) { @MainActor in
+                Task(priority: .utility) {
                     // Refresh from disk to pick up widget/watch changes
                     DataController.shared.refreshFromDisk()
 
@@ -124,17 +124,17 @@ struct FeelsApp: App {
                 }
 
                 // Defer Live Activity scheduling (heavy DB operations)
-                Task.detached(priority: .utility) {
+                Task(priority: .utility) {
                     await LiveActivityScheduler.shared.scheduleBasedOnCurrentTime()
                 }
 
                 // Catch up on side effects from widget/watch votes
-                Task.detached(priority: .utility) {
+                Task(priority: .utility) {
                     await MoodLogger.shared.processPendingSideEffects()
                 }
 
                 // Check subscription status (network call) - throttled
-                Task.detached(priority: .background) {
+                Task(priority: .background) {
                     await iapManager.checkSubscriptionStatus()
                     await iapManager.trackSubscriptionAnalytics(source: "app_foreground")
                 }