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/StabilityTests.swift

@@ -2,7 +2,7 @@
 //  StabilityTests.swift
 //  Tests iOS
 //
-//  Full navigation stability tests — visit every screen without crash.
+//  Full navigation stability tests -- visit every screen without crash.
 //
 
 import XCTest
@@ -10,67 +10,56 @@ import XCTest
 final class StabilityTests: BaseUITestCase {
     override var seedFixture: String? { "week_of_moods" }
 
-    /// TC-152: Navigate to every screen and feature without crashing.
-    func testFullNavigation_NoCrash() {
-        let tabBar = TabBarScreen(app: app)
-
-        // 1. Day tab (default) - verify loaded
-        assertTabSelected(tabBar.dayTab, name: "Day (initial)")
-        captureScreenshot(name: "stability_day")
-
-        // 2. Open entry detail
+    /// TC-152a: Open entry detail sheet and dismiss without crash.
+    func testStability_EntryDetail() {
         let firstEntry = app.firstEntryRow
-        if firstEntry.waitForExistence(timeout: 5) {
-            firstEntry.tapWhenReady()
-            let detailScreen = EntryDetailScreen(app: app)
-            if detailScreen.sheet.waitForExistence(timeout: 3) {
-                captureScreenshot(name: "stability_entry_detail")
-                detailScreen.dismiss()
-                detailScreen.assertDismissed()
-            }
-        }
+        firstEntry.waitForExistenceOrFail(timeout: navigationTimeout, message: "Entry row should exist from seeded data")
+        firstEntry.forceTap()
 
-        // 3. Month tab
-        tabBar.tapMonth()
-        assertTabSelected(tabBar.monthTab, name: "Month")
-        captureScreenshot(name: "stability_month")
-
-        // 4. Year tab
-        tabBar.tapYear()
-        assertTabSelected(tabBar.yearTab, name: "Year")
-        captureScreenshot(name: "stability_year")
-
-        // 5. Insights tab
-        tabBar.tapInsights()
-        assertTabSelected(tabBar.insightsTab, name: "Insights")
-        captureScreenshot(name: "stability_insights")
-
-        // 6. Settings tab - Customize sub-tab
-        tabBar.tapSettings()
-        assertTabSelected(tabBar.settingsTab, name: "Settings")
-        captureScreenshot(name: "stability_settings_customize")
-
-        // 7. Settings tab - Settings sub-tab
-        let settingsScreen = SettingsScreen(app: app)
-        settingsScreen.tapSettingsTab()
-        captureScreenshot(name: "stability_settings_settings")
-
-        // 8. Back to Customize sub-tab
-        settingsScreen.tapCustomizeTab()
-        captureScreenshot(name: "stability_settings_customize_return")
-
-        // 9. Back to Day
-        tabBar.tapDay()
-        assertTabSelected(tabBar.dayTab, name: "Day")
-
-        captureScreenshot(name: "stability_full_navigation_complete")
+        let detailScreen = EntryDetailScreen(app: app)
+        detailScreen.assertVisible()
+        detailScreen.dismiss()
+        detailScreen.assertDismissed()
     }
 
-    /// Wait for a tab to become selected (iOS 26 Liquid Glass may delay state updates).
-    private func assertTabSelected(_ tab: XCUIElement, name: String, timeout: TimeInterval = 8) {
-        let predicate = NSPredicate(format: "isSelected == true")
-        let expectation = XCTNSPredicateExpectation(predicate: predicate, object: tab)
-        let result = XCTWaiter.wait(for: [expectation], timeout: timeout)
-        XCTAssertEqual(result, .completed, "\(name) tab should be selected")
+    /// TC-152b: Navigate to Month tab without crash.
+    func testStability_MonthTab() {
+        let tabBar = TabBarScreen(app: app)
+        tabBar.tapMonth()
+        let monthGrid = app.element(UITestID.Month.grid)
+        monthGrid.waitForExistenceOrFail(timeout: navigationTimeout, message: "Month grid should be visible")
+    }
+
+    /// TC-152c: Navigate to Year tab without crash.
+    func testStability_YearTab() {
+        let tabBar = TabBarScreen(app: app)
+        tabBar.tapYear()
+        let heatmap = app.element(UITestID.Year.heatmap)
+        heatmap.waitForExistenceOrFail(timeout: navigationTimeout, message: "Year heatmap should be visible")
+    }
+
+    /// TC-152d: Navigate to Insights tab without crash.
+    func testStability_InsightsTab() {
+        let tabBar = TabBarScreen(app: app)
+        tabBar.tapInsights()
+        let insightsHeader = app.element(UITestID.Insights.header)
+        insightsHeader.waitForExistenceOrFail(timeout: navigationTimeout, message: "Insights header should be visible")
+    }
+
+    /// TC-152e: Navigate to Settings and switch sub-tabs without crash.
+    func testStability_SettingsTabs() {
+        let tabBar = TabBarScreen(app: app)
+        let settingsScreen = tabBar.tapSettings()
+        settingsScreen.assertVisible()
+        settingsScreen.tapSettingsTab()
+        settingsScreen.tapCustomizeTab()
+    }
+
+    /// TC-152f: Full round-trip back to Day tab without crash.
+    func testStability_ReturnToDay() {
+        let tabBar = TabBarScreen(app: app)
+        tabBar.tapSettings()
+        let dayScreen = tabBar.tapDay()
+        dayScreen.assertAnyEntryExists()
     }
 }