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/AppThemeTests.swift

@@ -22,28 +22,27 @@ final class AppThemeTests: BaseUITestCase {
 
     /// TC-070: Open Browse Themes sheet and verify all 12 theme cards exist.
     func testBrowseThemes_AllCardsExist() {
-        let tabBar = TabBarScreen(app: app)
-        let settingsScreen = tabBar.tapSettings()
+        let settingsScreen = TabBarScreen(app: app).tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
 
         let customizeScreen = CustomizeScreen(app: app)
-        XCTAssertTrue(customizeScreen.openThemePicker(), "Themes sheet should appear with theme cards")
+        customizeScreen.openThemePicker()
 
         // Verify all 12 theme cards are accessible (some may require scrolling)
         for theme in allThemes {
             let card = customizeScreen.appThemeCard(named: theme)
-            if !card.exists { _ = app.swipeUntilExists(card, direction: .up, maxSwipes: 6) }
-            XCTAssertTrue(
-                card.waitForExistence(timeout: 3),
-                "Theme card '\(theme)' should exist in the Browse Themes sheet"
+            card.scrollIntoView(in: app, direction: .up)
+            card.waitForExistenceOrFail(
+                timeout: defaultTimeout,
+                message: "Theme card '\(theme)' should exist in the Browse Themes sheet"
             )
         }
 
         captureScreenshot(name: "browse_themes_all_cards")
     }
 
-    /// TC-070: Apply a representative set of themes and verify no crash.
+    /// TC-070: Apply a theme and verify no crash.
     func testApplyThemes_NoCrash() {
         let tabBar = TabBarScreen(app: app)
         let settingsScreen = tabBar.tapSettings()
@@ -51,52 +50,26 @@ final class AppThemeTests: BaseUITestCase {
         settingsScreen.tapCustomizeTab()
 
         let customizeScreen = CustomizeScreen(app: app)
-        XCTAssertTrue(customizeScreen.openThemePicker(), "Browse Themes sheet should open")
+        customizeScreen.openThemePicker()
 
-        // Tap a representative sample of themes: first, middle, last
-        let sampled = ["Zen Garden", "Heartfelt", "Journal"]
-        for theme in sampled {
-            let card = customizeScreen.appThemeCard(named: theme)
-            if !card.exists { _ = app.swipeUntilExists(card, direction: .up, maxSwipes: 6) }
-            if card.waitForExistence(timeout: 3) {
-                card.tapWhenReady(timeout: 3)
+        // Tap a theme card, apply it
+        let card = customizeScreen.appThemeCard(named: "Zen Garden")
+        card.scrollIntoView(in: app, direction: .up)
+        card.forceTap()
 
-                // Apply theme via stable accessibility id.
-                let applyButton = app.element(UITestID.Customize.previewApplyButton)
-                if applyButton.waitForExistence(timeout: 3) {
-                    applyButton.tapWhenReady()
-                } else {
-                    let cancelButton = app.element(UITestID.Customize.previewCancelButton)
-                    if cancelButton.waitForExistence(timeout: 2) {
-                        cancelButton.tapWhenReady()
-                    }
-                }
-            }
-        }
+        // Apply via the preview apply button
+        let applyButton = app.element(UITestID.Customize.previewApplyButton)
+        applyButton.waitForExistenceOrFail(timeout: navigationTimeout, message: "Apply button should appear after tapping theme card")
+        applyButton.forceTap()
 
-        captureScreenshot(name: "themes_applied")
-
-        // Dismiss the themes sheet by swiping down or tapping Done
+        // Dismiss the themes sheet
         let doneButton = app.element(UITestID.Customize.pickerDoneButton)
-        if doneButton.waitForExistence(timeout: 2) {
-            doneButton.tapWhenReady()
-        } else {
-            // Swipe down to dismiss the sheet
-            app.swipeDown()
-        }
+        doneButton.waitForExistenceOrFail(timeout: navigationTimeout, message: "Done button should be visible to dismiss theme picker")
+        doneButton.forceTap()
 
-        // Wait for sheet dismissal — verify the sheet is actually gone
-        // by checking that the tab bar is accessible again
-        let tabBarElement = app.tabBars.firstMatch
-        if !tabBarElement.waitForExistence(timeout: 3) {
-            // Sheet may still be visible — try dismissing again
-            app.swipeDown()
-            _ = tabBarElement.waitForExistence(timeout: 3)
-        }
-
-        // Navigate to Day tab and verify no crash — entry row should still exist
+        // Navigate to Day tab and verify no crash
         tabBar.tapDay()
-        assertDayContentVisible(timeout: 10)
+        DayScreen(app: app).assertAnyEntryExists()
 
         captureScreenshot(name: "day_view_after_theme_change")
     }