Harden iOS app with audit fixes, UI consistency, and sheet race condition fixes

Applies verified fixes from deep audit (concurrency, performance, security,
accessibility), standardizes CRUD form buttons to Add/Save pattern, removes
.drawingGroup() that broke search bar TextFields, and converts vulnerable
.sheet(isPresented:) + if-let patterns to safe presentation to prevent
blank white modals.

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

iosApp/iosApp/PushNotifications/AppDelegate.swift

@@ -6,6 +6,10 @@ import ComposeApp
 @MainActor
 class AppDelegate: NSObject, UIApplicationDelegate, UNUserNotificationCenterDelegate {
 
+    /// Throttle subscription refreshes to at most once every 5 minutes
+    private static var lastSubscriptionRefresh: Date?
+    private static let subscriptionRefreshInterval: TimeInterval = 300 // 5 minutes
+
     func application(
         _ application: UIApplication,
         didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil
@@ -45,10 +49,17 @@ class AppDelegate: NSObject, UIApplicationDelegate, UNUserNotificationCenterDele
         // Clear badge when app becomes active
         PushNotificationManager.shared.clearBadge()
 
-        // Refresh StoreKit subscription status when app comes to foreground
+        // Refresh StoreKit subscription status when app comes to foreground (throttled to every 5 min)
         // This ensures we have the latest subscription state if it changed while app was in background
-        Task {
-            await StoreKitManager.shared.refreshSubscriptionStatus()
+        let now = Date()
+        if let lastRefresh = Self.lastSubscriptionRefresh,
+           now.timeIntervalSince(lastRefresh) < Self.subscriptionRefreshInterval {
+            // Skip — refreshed recently
+        } else {
+            Self.lastSubscriptionRefresh = now
+            Task {
+                await StoreKitManager.shared.refreshSubscriptionStatus()
+            }
         }
     }