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/AllDayViewStylesTests.swift

@@ -2,7 +2,7 @@
 //  AllDayViewStylesTests.swift
 //  Tests iOS
 //
-//  Exhaustive day view style switching tests — verify all 20 styles render without crash.
+//  Exhaustive day view style switching tests -- verify styles render without crash.
 //
 
 import XCTest
@@ -12,26 +12,22 @@ final class AllDayViewStylesTests: BaseUITestCase {
     override var bypassSubscription: Bool { true }
 
     /// TC-021: Switch between representative day view styles and verify no crash.
-    /// Tests a sample of 5 styles (first, middle, last, and edge cases) to verify
-    /// stability without exhaustively cycling all 20, which can cause resource pressure.
     func testAllDayViewStyles_NoCrash() {
         let tabBar = TabBarScreen(app: app)
         let customizeScreen = CustomizeScreen(app: app)
+        let dayScreen = DayScreen(app: app)
 
-        // Representative sample: first, a middle one, last, and two requiring scroll
         let sampleStyles = ["Classic", "Neon", "Glass", "Orbit", "Minimal"]
 
         for style in sampleStyles {
-            // Navigate to Settings > Customize tab
             let settingsScreen = tabBar.tapSettings()
             settingsScreen.assertVisible()
             settingsScreen.tapCustomizeTab()
 
             customizeScreen.selectDayViewStyle(style)
 
-            // Navigate to Day tab and verify the app didn't crash
             tabBar.tapDay()
-            assertDayContentVisible()
+            dayScreen.assertAnyEntryExists()
         }
 
         captureScreenshot(name: "all_day_view_styles_completed")