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/Services/ImageCache.swift

@@ -15,13 +15,15 @@ final class ImageCache {
     private let cache = NSCache<NSString, UIImage>()
     private let queue = DispatchQueue(label: "com.tt.feels.imagecache", qos: .userInitiated)
 
+    private var memoryWarningToken: NSObjectProtocol?
+
     private init() {
         // Configure cache limits
         cache.countLimit = 100 // Max 100 images
         cache.totalCostLimit = 50 * 1024 * 1024 // 50 MB max
 
         // Clear cache on memory warning
-        NotificationCenter.default.addObserver(
+        memoryWarningToken = NotificationCenter.default.addObserver(
             forName: UIApplication.didReceiveMemoryWarningNotification,
             object: nil,
             queue: .main
@@ -30,6 +32,12 @@ final class ImageCache {
         }
     }
 
+    deinit {
+        if let token = memoryWarningToken {
+            NotificationCenter.default.removeObserver(token)
+        }
+    }
+
     // MARK: - Public API
 
     /// Get image from cache