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/CustomizationTests.swift

@@ -13,14 +13,11 @@ final class CustomizationTests: BaseUITestCase {
 
     /// TC-071: Switch between all 4 theme modes without crashing.
     func testThemeModes_AllSelectable() {
-        let tabBar = TabBarScreen(app: app)
-        let settingsScreen = tabBar.tapSettings()
+        let settingsScreen = TabBarScreen(app: app).tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
-        let customizeScreen = CustomizeScreen(app: app)
 
-        // Should already be on Customize sub-tab
-        // Theme buttons are: System, iFeel, Dark, Light
+        let customizeScreen = CustomizeScreen(app: app)
         let themeNames = ["System", "iFeel", "Dark", "Light"]
 
         for themeName in themeNames {
@@ -36,9 +33,8 @@ final class CustomizationTests: BaseUITestCase {
         let settingsScreen = tabBar.tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
-        let customizeScreen = CustomizeScreen(app: app)
 
-        // Voting layout names (from VotingLayoutStyle enum)
+        let customizeScreen = CustomizeScreen(app: app)
         let layouts = ["Horizontal", "Cards", "Stacked", "Aura", "Orbit", "Neon"]
 
         for layout in layouts {
@@ -47,9 +43,10 @@ final class CustomizationTests: BaseUITestCase {
 
         captureScreenshot(name: "voting_layouts_cycled")
 
-        // Navigate to Day tab to verify the voting layout renders
+        // Navigate to Day tab and verify the voting layout renders
         tabBar.tapDay()
-        assertDayContentVisible()
+        DayScreen(app: app).assertAnyEntryExists()
+
         captureScreenshot(name: "day_view_after_layout_change")
     }
 
@@ -59,9 +56,8 @@ final class CustomizationTests: BaseUITestCase {
         let settingsScreen = tabBar.tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
-        let customizeScreen = CustomizeScreen(app: app)
 
-        // Test a representative sample of day view styles (testing all 20+ would be slow)
+        let customizeScreen = CustomizeScreen(app: app)
         let styles = ["Classic", "Minimal", "Compact", "Bubble", "Grid", "Neon"]
 
         for style in styles {
@@ -70,9 +66,9 @@ final class CustomizationTests: BaseUITestCase {
 
         captureScreenshot(name: "day_styles_cycled")
 
-        // Navigate to Day tab to verify the style renders with data
+        // Navigate to Day tab and verify the style renders with data
         tabBar.tapDay()
-        assertDayContentVisible()
+        DayScreen(app: app).assertAnyEntryExists()
 
         captureScreenshot(name: "day_view_after_style_change")
     }