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/EntryListView.swift

@@ -2224,6 +2224,9 @@ struct MotionCardView: View {
         .onAppear {
             motionManager.startIfNeeded()
         }
+        .onDisappear {
+            motionManager.stopIfNoConsumers()
+        }
     }
 }
 
@@ -2237,10 +2240,13 @@ class MotionManager: ObservableObject {
     @Published var yOffset: CGFloat = 0
 
     private var isRunning = false
+    private var activeConsumers = 0
 
     private init() {}
 
     func startIfNeeded() {
+        activeConsumers += 1
+
         guard !isRunning,
               motionManager.isDeviceMotionAvailable,
               !UIAccessibility.isReduceMotionEnabled else { return }
@@ -2257,8 +2263,18 @@ class MotionManager: ObservableObject {
         }
     }
 
+    func stopIfNoConsumers() {
+        activeConsumers = max(0, activeConsumers - 1)
+        guard activeConsumers == 0, isRunning else { return }
+        isRunning = false
+        motionManager.stopDeviceMotionUpdates()
+        xOffset = 0
+        yOffset = 0
+    }
+
     func stop() {
         guard isRunning else { return }
+        activeConsumers = 0
         isRunning = false
         motionManager.stopDeviceMotionUpdates()
     }