Fix remaining 9 UI test failures: subscription state, scroll, timing

- Replace removePersistentDomain with key-by-key removal in resetAppState
  (removePersistentDomain is unreliable on app group UserDefaults suites)
- Add explicit cache clearing in IAPManager.resetForTesting() to prevent
  stale cachedSubscriptionExpiration from restoring .subscribed state
- Use descendants(matching: .any) for upgrade_banner and subscribe_button
  queries (VStack may not match otherElements in SwiftUI)
- Add multiple swipe attempts for icon pack horizontal scroll
- Use coordinate-based drag for onboarding paged TabView advancement
- Add longer wait for Day view refresh after theme change
- Add multiple scroll attempts to find clear data button in Settings

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

Tests iOS/IconPackTests.swift

@@ -35,14 +35,25 @@ final class IconPackTests: BaseUITestCase {
 
         for pack in allIconPacks {
             let button = app.buttons["customize_iconpack_\(pack)"]
-            if !button.exists {
-                // Icon packs may be in a horizontal scroll — try swipe left first
+
+            // Icon packs are in a horizontal scroll view.
+            // Try multiple scroll strategies to find the button.
+            if !button.waitForExistence(timeout: 2) {
+                // Try swiping left in the horizontal scroll area
                 app.swipeLeft()
             }
-            if !button.exists {
-                // If still not found, try scrolling the page down
+            if !button.waitForExistence(timeout: 1) {
+                app.swipeLeft()
+            }
+            if !button.waitForExistence(timeout: 1) {
+                // Try scrolling the page down to reveal the icon pack section
                 app.swipeUp()
             }
+            if !button.waitForExistence(timeout: 1) {
+                // Try swiping left again after scrolling down
+                app.swipeLeft()
+            }
+
             if button.waitForExistence(timeout: 3) {
                 button.coordinate(withNormalizedOffset: CGVector(dx: 0.5, dy: 0.5)).tap()
             } else {