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/IconPackTests.swift

@@ -29,37 +29,36 @@ final class IconPackTests: BaseUITestCase {
         let settingsScreen = tabBar.tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
+
         let customizeScreen = CustomizeScreen(app: app)
 
         for pack in allIconPacks {
             customizeScreen.selectIconPack(pack)
-            XCTAssertTrue(customizeScreen.iconPackButton(named: pack).exists, "Icon pack button '\(pack)' should exist in the customize view")
         }
 
         captureScreenshot(name: "icon_packs_cycled")
 
-        // Navigate to Day tab and verify no crash — entry row should still exist
+        // Navigate to Day tab and verify no crash
         tabBar.tapDay()
-
-        assertDayContentVisible()
+        DayScreen(app: app).assertAnyEntryExists()
 
         captureScreenshot(name: "day_view_after_icon_pack_change")
     }
 
     /// TC-072: Verify each icon pack button exists in the customize view.
     func testIconPacks_AllButtonsExist() {
-        let tabBar = TabBarScreen(app: app)
-        let settingsScreen = tabBar.tapSettings()
+        let settingsScreen = TabBarScreen(app: app).tapSettings()
         settingsScreen.assertVisible()
         settingsScreen.tapCustomizeTab()
+
         let customizeScreen = CustomizeScreen(app: app)
 
         for pack in allIconPacks {
             let button = customizeScreen.iconPackButton(named: pack)
-            if !button.exists { _ = app.swipeUntilExists(button, direction: .up, maxSwipes: 6) }
-            XCTAssertTrue(
-                button.waitForExistence(timeout: 3),
-                "Icon pack button '\(pack)' should exist"
+            button.scrollIntoView(in: app, direction: .up)
+            button.waitForExistenceOrFail(
+                timeout: defaultTimeout,
+                message: "Icon pack button '\(pack)' should exist"
             )
         }