Add XCUITest suite with 27 test files covering unmapped P1 test cases

- Add 8 new test files: HeaderMoodLogging (TC-002), DayViewGrouping (TC-019),
  AllDayViewStyles (TC-021), MonthViewInteraction (TC-030), PaywallGate
  (TC-032/039/048), AppTheme (TC-070), IconPack (TC-072),
  PremiumCustomization (TC-075)
- Add accessibility IDs for paywall overlays, icon packs, app theme cards,
  and day view section headers
- Add --expire-trial launch argument to UITestMode for paywall gate testing
- Update QA test plan spreadsheet with XCUITest names for 14 test cases
- Include existing test infrastructure: screen objects, helpers, base class,
  and 19 previously written test files

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

Shared/Onboarding/views/OnboardingSubscription.swift

@@ -117,6 +117,7 @@ struct OnboardingSubscription: View {
                     }
                     .accessibilityLabel(String(localized: "Get Personal Insights"))
                     .accessibilityHint(String(localized: "Opens subscription options"))
+                    .accessibilityIdentifier(AccessibilityID.Onboarding.subscribeButton)
 
                     // Skip button
                     Button(action: {
@@ -130,12 +131,14 @@ struct OnboardingSubscription: View {
                     }
                     .accessibilityLabel(String(localized: "Maybe Later"))
                     .accessibilityHint(String(localized: "Skip subscription and complete setup"))
+                    .accessibilityIdentifier(AccessibilityID.Onboarding.skipButton)
                     .padding(.top, 4)
                 }
                 .padding(.horizontal, 24)
                 .padding(.bottom, 50)
             }
         }
+        .accessibilityIdentifier(AccessibilityID.Onboarding.subscriptionScreen)
         .sheet(isPresented: $showSubscriptionStore, onDismiss: {
             // After subscription store closes, complete onboarding
             AnalyticsManager.shared.track(.onboardingCompleted(dayId: nil))