Fix 4 flaky UI tests for iOS 26 compatibility

- AppLaunchTests/StabilityTests: Increase assertTabSelected timeout to
  8s for iOS 26 Liquid Glass delayed isSelected state updates
- DeepLinkTests: Detect SubscriptionStoreView container instead of text
  labels, since Apple's native view shows "Subscription Unavailable" in
  test storefront
- SettingsActionTests: Check for empty state after clearing data, bump
  Settings header timeout to 8s

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

Tests iOS/Screens/SettingsScreen.swift

@@ -53,7 +53,7 @@ struct SettingsScreen {
 
     func assertVisible(file: StaticString = #file, line: UInt = #line) {
         XCTAssertTrue(
-            settingsHeader.waitForExistence(timeout: 5),
+            settingsHeader.waitForExistence(timeout: 8),
             "Settings header should be visible",
             file: file, line: line
         )