Harden iOS app: fix concurrency, animations, formatters, privacy, and logging

- Eliminate NumberFormatters shared singleton data race; use local formatters
- Add reduceMotion checks to empty-state animations in 3 list views
- Wrap 68+ print() statements in #if DEBUG across push notification code
- Remove redundant .receive(on: DispatchQueue.main) in SubscriptionCache
- Remove redundant initializeLookups() call from iOSApp.init()
- Clean up StoreKitManager Task capture in listenForTransactions()
- Add memory warning observer to AuthenticatedImage cache
- Cache parseContent result in UpgradePromptView init
- Add DiskSpace and FileTimestamp API declarations to Privacy Manifest
- Add FIXME for analytics debug/production API key separation
- Use static formatter in PropertyHeaderCard

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/iosApp/Helpers/ThemeManager.swift

@@ -61,7 +61,15 @@ enum ThemeID: String, CaseIterable, Codable {
 
 // MARK: - Shared App Group UserDefaults
 private let appGroupID = "group.com.tt.casera.CaseraDev"
-private let sharedDefaults = UserDefaults(suiteName: appGroupID) ?? UserDefaults.standard
+private let sharedDefaults: UserDefaults = {
+    guard let defaults = UserDefaults(suiteName: appGroupID) else {
+        #if DEBUG
+        assertionFailure("App Group '\(appGroupID)' not configured — theme won't sync to widgets")
+        #endif
+        return UserDefaults.standard
+    }
+    return defaults
+}()
 
 // MARK: - Theme Manager
 #if WIDGET_EXTENSION
@@ -84,6 +92,7 @@ class ThemeManager {
 }
 #else
 // Full ThemeManager for main app with ObservableObject support
+@MainActor
 class ThemeManager: ObservableObject {
     static let shared = ThemeManager()