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/Views/MonthView/MonthView.swift

@@ -327,6 +327,7 @@ struct MonthView: View {
                 .frame(maxWidth: .infinity)
                 .background(theme.currentTheme.bg)
                 .frame(maxHeight: .infinity, alignment: .bottom)
+                .accessibilityIdentifier(AccessibilityID.Paywall.monthOverlay)
             } else if iapManager.shouldShowTrialWarning && !demoManager.isDemoMode {
                 VStack {
                     Spacer()