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/Utilities/AccessibilityHelpers.swift

@@ -21,25 +21,7 @@ extension EnvironmentValues {
     }
 }
 
-/// View modifier that respects reduce motion preference
-struct ReduceMotionModifier: ViewModifier {
-    @Environment(\.accessibilityReduceMotion) var reduceMotion
-
-    let animation: Animation?
-    let reducedAnimation: Animation?
-
-    func body(content: Content) -> some View {
-        content
-            .animation(reduceMotion ? reducedAnimation : animation, value: UUID())
-    }
-}
-
 extension View {
-    /// Applies animation only when reduce motion is disabled
-    func accessibleAnimation(_ animation: Animation? = .default, reduced: Animation? = nil) -> some View {
-        modifier(ReduceMotionModifier(animation: animation, reducedAnimation: reduced))
-    }
-
     /// Wraps content in withAnimation respecting reduce motion
     func withAccessibleAnimation<V: Equatable>(_ animation: Animation? = .default, value: V, action: @escaping () -> Void) -> some View {
         self.onChange(of: value) { _, _ in
@@ -59,11 +41,10 @@ extension View {
 extension View {
     /// Adds accessibility label with optional hint
     func accessibleMoodCell(mood: Mood, date: Date) -> some View {
-        let formatter = DateFormatter()
-        formatter.dateStyle = .medium
+        let dateString = DateFormattingCache.shared.string(for: date, format: .dateMedium)
 
         return self
-            .accessibilityLabel("\(mood.strValue) on \(formatter.string(from: date))")
+            .accessibilityLabel("\(mood.strValue) on \(dateString)")
             .accessibilityHint("Double tap to edit mood")
     }