Add comprehensive WCAG 2.1 AA accessibility support

- Add VoiceOver labels and hints to all voting layouts, settings, widgets,
  onboarding screens, and entry cells
- Add Reduce Motion support to button animations throughout the app
- Ensure 44x44pt minimum touch targets on widget mood buttons
- Enhance AccessibilityHelpers with Dynamic Type support, ScaledValue wrapper,
  and VoiceOver detection utilities
- Gate premium features (Insights, Month/Year views) behind subscription
- Update widgets to show subscription prompts for non-subscribers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Shared/IAPManager.swift

@@ -25,6 +25,11 @@ enum SubscriptionState: Equatable {
 @MainActor
 class IAPManager: ObservableObject {
 
+    // MARK: - Shared Instance
+
+    /// Shared instance for service-level access (e.g., HealthKit gating)
+    static let shared = IAPManager()
+
     // MARK: - Debug Toggle
 
     /// Set to `true` to bypass all subscription checks and grant full access (for development only)