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/OnboardingTests.swift

@@ -46,16 +46,32 @@ final class OnboardingTests: BaseUITestCase {
         swipeAndWait() // Style → Subscription
         captureScreenshot(name: "onboarding_subscription")
 
-        // Tap "Maybe Later" to complete onboarding
+        // Find the "Maybe Later" skip button on the subscription screen.
+        // Try multiple approaches in case the page transition didn't complete.
         let skipButton = app.descendants(matching: .any)
             .matching(identifier: "onboarding_skip_button")
             .firstMatch
 
-        // If skip button isn't visible, try one more swipe (in case a page was added)
-        if !skipButton.waitForExistence(timeout: 5) {
+        // If skip button isn't visible, try additional swipes
+        for _ in 0..<3 {
+            if skipButton.waitForExistence(timeout: 3) { break }
             swipeAndWait()
         }
 
+        // Also try finding by label as a fallback
+        if !skipButton.exists {
+            let maybeLater = app.buttons.matching(
+                NSPredicate(format: "label CONTAINS[cd] %@", "Maybe Later")
+            ).firstMatch
+            if maybeLater.waitForExistence(timeout: 3) {
+                maybeLater.coordinate(withNormalizedOffset: CGVector(dx: 0.5, dy: 0.5)).tap()
+                let tabBar = app.tabBars.firstMatch
+                XCTAssertTrue(tabBar.waitForExistence(timeout: 10), "Tab bar should appear after onboarding")
+                captureScreenshot(name: "onboarding_complete")
+                return
+            }
+        }
+
         XCTAssertTrue(
             skipButton.waitForExistence(timeout: 5),
             "Skip/Maybe Later button should exist on subscription screen"