Rewrite all UI tests following fail-fast TEST_RULES patterns

Rewrote 60+ test files to follow honeydue-style test guidelines:
- defaultTimeout=2s, navigationTimeout=5s — fail fast, no long waits
- No coordinate taps (except onboarding paged TabView swipes)
- No sleep(), no retry loops
- No guard...else { return } silent passes — XCTFail everywhere
- All elements by accessibility ID via UITestID constants
- Screen objects for all navigation/actions/assertions
- One logical assertion per test method

Added missing accessibility identifiers to app views:
- MonthView.swift: added AccessibilityID.MonthView.grid to ScrollView
- YearView.swift: added AccessibilityID.YearView.heatmap to ScrollView

Framework rewrites:
- BaseUITestCase: added session ID, localeArguments, extraLaunchArguments
- WaitHelpers: waitForExistenceOrFail, waitUntilHittableOrFail,
  waitForNonExistence, scrollIntoView, forceTap
- All 7 screen objects rewritten with fail-fast semantics
- TEST_RULES.md added with non-negotiable rules

Known remaining issues:
- OnboardingTests: paged TabView swipes unreliable on iOS 26 simulator
- SettingsLegalLinksTests: EULA/Privacy buttons too deep in DEBUG scroll
- Customization horizontal picker scrolling needs further tuning

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Tests iOS/EmptyStateTests.swift

@@ -10,29 +10,30 @@ 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.
+    /// TC-020: With no entries, mood header or empty state text is visible.
+    func testEmptyState_ShowsMoodHeaderOrNoData() {
         let moodHeader = app.element(UITestID.Day.moodHeader)
         let noDataText = app.element(UITestID.Day.emptyStateNoData)
 
-        // At least one of these should be visible
-        let headerExists = moodHeader.waitForExistence(timeout: 5)
-        let noDataExists = noDataText.waitForExistence(timeout: 2)
+        let headerExists = moodHeader.waitForExistence(timeout: navigationTimeout)
+        if !headerExists {
+            noDataText.waitForExistenceOrFail(
+                timeout: defaultTimeout,
+                message: "Either mood header or 'no data' text should be visible in empty state"
+            )
+        }
+    }
 
-        XCTAssertTrue(
-            headerExists || noDataExists,
-            "Either mood header or 'no data' text should be visible in empty state"
-        )
+    /// TC-020b: With no entries, no entry rows exist.
+    func testEmptyState_NoEntryRows() {
+        // Wait for the app to settle by confirming some content is visible
+        let moodHeader = app.element(UITestID.Day.moodHeader)
+        moodHeader.waitForExistenceOrFail(timeout: navigationTimeout, message: "Day screen should be loaded")
 
-        // No entry rows should exist
-        let entryRows = app.firstEntryRow
+        let entryRow = app.firstEntryRow
         XCTAssertFalse(
-            entryRows.waitForExistence(timeout: 2),
+            entryRow.waitForExistence(timeout: defaultTimeout),
             "No entry rows should exist in empty state"
         )
-
-        captureScreenshot(name: "empty_state")
     }
 }