Refactor ZStack layouts to .background(), add Year View accessibility IDs, triage QA test plan

Replace ZStack-with-gradient patterns with idiomatic .background() modifier
across onboarding, customize, and settings views. Add accessibility identifiers
to Year View charts for UI test automation. Mark 67 impossible-to-automate
tests RED in QA plan and scaffold initial Year View and Settings onboarding tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Tests iOS/SettingsOnboardingTests.swift

@@ -0,0 +1,48 @@
+//
+//  SettingsOnboardingTests.swift
+//  Tests iOS
+//
+//  TC-124: Show onboarding from Settings.
+//
+
+import XCTest
+
+final class SettingsOnboardingTests: BaseUITestCase {
+    override var seedFixture: String? { "empty" }
+    override var bypassSubscription: Bool { true }
+
+    /// TC-124: Tapping Show Onboarding in Settings replays the onboarding flow.
+    func testSettings_ShowOnboarding_OpensOnboardingFlow() {
+        let tabBar = TabBarScreen(app: app)
+        let settingsScreen = tabBar.tapSettings()
+        settingsScreen.assertVisible()
+
+        // Switch to the Settings sub-tab (not Customize)
+        settingsScreen.tapSettingsTab()
+
+        captureScreenshot(name: "settings_before_show_onboarding")
+
+        // Scroll to and tap "Show Onboarding" button
+        let showOnboardingBtn = app.element("settings_show_onboarding")
+        guard showOnboardingBtn.waitForExistence(timeout: 2) ||
+                app.swipeUntilExists(showOnboardingBtn, direction: .up, maxSwipes: 8) else {
+            captureScreenshot(name: "settings_show_onboarding_not_found")
+            XCTFail("Show Onboarding button not found in Settings")
+            return
+        }
+        showOnboardingBtn.tapWhenReady()
+
+        // The sheet may take a moment to animate in.
+        // Look for the onboarding welcome screen or any text unique to onboarding.
+        let welcomeScreen = app.element(UITestID.Onboarding.welcome)
+        let welcomeText = app.staticTexts["Welcome to Feels"]
+        let found = welcomeScreen.waitForExistence(timeout: 8) ||
+                    welcomeText.waitForExistence(timeout: 3)
+
+        captureScreenshot(name: "settings_show_onboarding_result")
+
+        XCTAssertTrue(found,
+            "Onboarding should appear after tapping Show Onboarding"
+        )
+    }
+}