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/EmptyStateTests.swift

@@ -0,0 +1,40 @@
+//
+//  EmptyStateTests.swift
+//  Tests iOS
+//
+//  Empty state display tests.
+//
+
+import XCTest
+
+final class EmptyStateTests: BaseUITestCase {
+    override var seedFixture: String? { "empty" }
+
+    /// TC-020: With no entries, the empty state should display without crashing.
+    func testEmptyState_ShowsNoDataMessage() {
+        // The app should show either the mood header (voting prompt) or
+        // the empty state text. Either way, it should not crash.
+        let moodHeader = app.otherElements["mood_header"]
+        let noDataText = app.staticTexts["empty_state_no_data"]
+
+        // At least one of these should be visible
+        let headerExists = moodHeader.waitForExistence(timeout: 5)
+        let noDataExists = noDataText.waitForExistence(timeout: 2)
+
+        XCTAssertTrue(
+            headerExists || noDataExists,
+            "Either mood header or 'no data' text should be visible in empty state"
+        )
+
+        // No entry rows should exist
+        let entryRows = app.descendants(matching: .any)
+            .matching(NSPredicate(format: "identifier BEGINSWITH %@", "entry_row_"))
+            .firstMatch
+        XCTAssertFalse(
+            entryRows.waitForExistence(timeout: 2),
+            "No entry rows should exist in empty state"
+        )
+
+        captureScreenshot(name: "empty_state")
+    }
+}