Add onboarding Next buttons and fix accessibility for paged TabView

App-side changes:
- Added "Get Started" / "Continue" next buttons to all onboarding pages
  (Welcome, Day, Time, Style) with onboarding_next_button accessibility ID
- Added onNext callback plumbing from OnboardingMain to each page
- OnboardingMain now uses TabView(selection:) for programmatic page navigation
- Added .accessibilityElement(children: .contain) to all onboarding pages
  to fix iOS 26 paged TabView not exposing child elements
- Added settings_segmented_picker accessibility ID to Settings Picker
- Reduced padding on onboarding pages to keep buttons in visible area

Test-side changes:
- OnboardingScreen: replaced unreliable swipeToNext() with tapNext()
  that taps the accessibility-identified next button
- OnboardingScreen: multi-strategy skip button detection for subscription page
- SettingsScreen: scoped segment tap to picker element to avoid tab bar collision
- CustomizeScreen: simplified horizontal scroll to plain app.swipeLeft()
- OnboardingVotingTests: uses tapNext() to advance to Day page

Passing: OnboardingTests.CompleteFlow, OnboardingVotingTests
Remaining: OnboardingTests.DoesNotRepeat (session state issue),
  Settings scroll (deep elements), Customize horizontal pickers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Shared/Onboarding/views/OnboardingWelcome.swift

@@ -8,6 +8,8 @@
 import SwiftUI
 
 struct OnboardingWelcome: View {
+    var onNext: (() -> Void)? = nil
+
     var body: some View {
         ZStack {
             // Gradient background
@@ -54,28 +56,32 @@ struct OnboardingWelcome: View {
                 Spacer()
 
                 // Feature highlights
-                VStack(spacing: 20) {
+                VStack(spacing: 16) {
                     FeatureRow(icon: "bell.badge.fill", title: "Daily Reminders", description: "Never forget to log your mood")
                     FeatureRow(icon: "chart.bar.fill", title: "Beautiful Insights", description: "See your mood patterns over time")
                     FeatureRow(icon: "paintpalette.fill", title: "Fully Customizable", description: "Make it yours with themes & colors")
                 }
                 .padding(.horizontal, 30)
-                .padding(.bottom, 40)
+                .padding(.bottom, 24)
 
-                // Swipe hint
-                HStack(spacing: 8) {
-                    Text("Swipe to get started")
-                        .font(.subheadline.weight(.medium))
-                        .foregroundColor(.white.opacity(0.7))
-                    Image(systemName: "chevron.right")
-                        .font(.subheadline.weight(.semibold))
-                        .foregroundColor(.white.opacity(0.7))
+                // Continue button
+                Button(action: { onNext?() }) {
+                    Text("Get Started")
+                        .font(.headline.weight(.semibold))
+                        .foregroundColor(Color(hex: "667eea"))
+                        .frame(maxWidth: .infinity)
+                        .padding(.vertical, 14)
+                        .background(
+                            RoundedRectangle(cornerRadius: 16)
+                                .fill(.white)
+                        )
                 }
-                .padding(.bottom, 60)
-                .accessibilityLabel(String(localized: "Swipe right to continue"))
-                .accessibilityHint(String(localized: "Swipe to the next onboarding step"))
+                .padding(.horizontal, 30)
+                .padding(.bottom, 40)
+                .accessibilityIdentifier(AccessibilityID.Onboarding.nextButton)
             }
         }
+        .accessibilityElement(children: .contain)
         .accessibilityIdentifier(AccessibilityID.Onboarding.welcomeScreen)
     }
 }