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/FeelsApp.swift

@@ -24,6 +24,11 @@ struct FeelsApp: App {
     @State private var showStorageFallbackAlert = SharedModelContainer.isUsingInMemoryFallback
 
     init() {
+        // Configure UI test mode before anything else
+        if UITestMode.isUITesting {
+            UITestMode.configureIfNeeded()
+        }
+
         AnalyticsManager.shared.configure()
 
         BGTaskScheduler.shared.cancelAllTaskRequests()