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>

Tests iOS/DataPersistenceTests.swift

@@ -0,0 +1,51 @@
+//
+//  DataPersistenceTests.swift
+//  Tests iOS
+//
+//  Data persistence tests — verify entries survive app relaunch.
+//
+
+import XCTest
+
+final class DataPersistenceTests: BaseUITestCase {
+    override var seedFixture: String? { "empty" }
+
+    /// TC-156: Log a mood, force quit, relaunch → entry should persist.
+    func testDataPersists_AcrossRelaunch() {
+        let dayScreen = DayScreen(app: app)
+
+        // Log a mood
+        dayScreen.assertMoodHeaderVisible()
+        dayScreen.logMood(.great)
+
+        // Verify entry was created
+        let greatEntry = app.descendants(matching: .any)
+            .matching(NSPredicate(format: "label CONTAINS[cd] %@", "Great"))
+            .firstMatch
+        XCTAssertTrue(
+            greatEntry.waitForExistence(timeout: 8),
+            "Entry should appear after logging"
+        )
+
+        captureScreenshot(name: "before_relaunch")
+
+        // Terminate the app
+        app.terminate()
+
+        // Relaunch WITHOUT --reset-state to preserve data
+        let freshApp = XCUIApplication()
+        freshApp.launchArguments = ["--ui-testing", "--disable-animations", "--bypass-subscription", "--skip-onboarding"]
+        freshApp.launch()
+
+        // The entry should still exist after relaunch
+        let entryRow = freshApp.descendants(matching: .any)
+            .matching(NSPredicate(format: "identifier BEGINSWITH %@", "entry_row_"))
+            .firstMatch
+        XCTAssertTrue(
+            entryRow.waitForExistence(timeout: 8),
+            "Entry should persist after force quit and relaunch"
+        )
+
+        captureScreenshot(name: "after_relaunch_data_persists")
+    }
+}