Fix cascading crash and remaining UI test failures

- Revert key-by-key UserDefaults iteration that removed system keys
  causing kAXErrorServerNotFound crashes; restore removePersistentDomain
  with explicit subscription key clearing
- Add .accessibilityElement(children: .contain) to UpgradeBannerView
  so subscribe button is discoverable by XCUITest
- Fix AllDayViewStylesTests to use coordinate-based tapping instead of
  button.isHittable/button.tap() for iOS 26 Liquid Glass compatibility
- Improve OnboardingTests with multiple swipe retries and label-based
  fallback for skip button

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

Tests iOS/AllDayViewStylesTests.swift

@@ -29,22 +29,21 @@ final class AllDayViewStylesTests: BaseUITestCase {
             settingsScreen.assertVisible()
             settingsScreen.tapCustomizeTab()
 
-            // Try to find and tap the style button, scrolling if needed
+            // Try to find the style button, scrolling if needed
             let button = customizeScreen.dayViewStyleButton(named: style)
-            if !button.waitForExistence(timeout: 2) || !button.isHittable {
-                // Scroll left multiple times to find styles further right
+            if !button.waitForExistence(timeout: 2) {
+                // Scroll left multiple times to find styles further right in horizontal scroll
                 for _ in 0..<5 {
                     app.swipeLeft()
-                    if button.isHittable { break }
+                    if button.waitForExistence(timeout: 1) { break }
                 }
             }
 
-            if button.isHittable {
-                button.tap()
-            } else {
-                // Style button not found after scrolling — skip but don't fail,
-                // as the main assertion is no-crash on the Day tab
+            if button.waitForExistence(timeout: 2) {
+                // Use coordinate tap for iOS 26 Liquid Glass compatibility
+                button.coordinate(withNormalizedOffset: CGVector(dx: 0.5, dy: 0.5)).tap()
             }
+            // Skip but don't fail if button not found — main assertion is no-crash
 
             // Navigate to Day tab and verify the entry row still renders
             tabBar.tapDay()