feat: onboarding flow with staggered-reveal wow screen

6-screen conversion funnel: Problem → Empathy → Solution → Wow → Personalization → Paywall.
Screen 4 uses a staggered-reveal feature list where all 4 features animate in
sequentially (150ms apart), replacing a carousel pattern.

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

src/shared/components/OnboardingStep.tsx

@@ -0,0 +1,108 @@
+/**
+ * TabataFit OnboardingStep
+ * Reusable wrapper for each onboarding screen — progress bar, animation, layout
+ */
+
+import { useRef, useEffect } from 'react'
+import { View, StyleSheet, Animated, Dimensions } from 'react-native'
+import { useSafeAreaInsets } from 'react-native-safe-area-context'
+import { DARK, BRAND, TEXT } from '../constants/colors'
+import { SPACING, LAYOUT } from '../constants/spacing'
+import { DURATION, EASE } from '../constants/animations'
+
+const { width: SCREEN_WIDTH } = Dimensions.get('window')
+
+interface OnboardingStepProps {
+  step: number
+  totalSteps: number
+  children: React.ReactNode
+}
+
+export function OnboardingStep({ step, totalSteps, children }: OnboardingStepProps) {
+  const insets = useSafeAreaInsets()
+  const slideAnim = useRef(new Animated.Value(SCREEN_WIDTH)).current
+  const fadeAnim = useRef(new Animated.Value(0)).current
+  const progressAnim = useRef(new Animated.Value(0)).current
+
+  useEffect(() => {
+    // Reset position for new step
+    slideAnim.setValue(SCREEN_WIDTH)
+    fadeAnim.setValue(0)
+
+    // Animate in
+    Animated.parallel([
+      Animated.timing(slideAnim, {
+        toValue: 0,
+        duration: DURATION.NORMAL,
+        easing: EASE.EASE_OUT,
+        useNativeDriver: true,
+      }),
+      Animated.timing(fadeAnim, {
+        toValue: 1,
+        duration: DURATION.NORMAL,
+        easing: EASE.EASE_OUT,
+        useNativeDriver: true,
+      }),
+    ]).start()
+
+    // Animate progress bar
+    Animated.timing(progressAnim, {
+      toValue: step / totalSteps,
+      duration: DURATION.SLOW,
+      easing: EASE.EASE_OUT,
+      useNativeDriver: false,
+    }).start()
+  }, [step])
+
+  const progressWidth = progressAnim.interpolate({
+    inputRange: [0, 1],
+    outputRange: ['0%', '100%'],
+  })
+
+  return (
+    <View style={[styles.container, { paddingTop: insets.top + SPACING[3] }]}>
+      {/* Progress bar */}
+      <View style={styles.progressTrack}>
+        <Animated.View style={[styles.progressFill, { width: progressWidth }]} />
+      </View>
+
+      {/* Step content */}
+      <Animated.View
+        style={[
+          styles.content,
+          {
+            transform: [{ translateX: slideAnim }],
+            opacity: fadeAnim,
+          },
+          { paddingBottom: insets.bottom + SPACING[6] },
+        ]}
+      >
+        {children}
+      </Animated.View>
+    </View>
+  )
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    backgroundColor: DARK.BASE,
+  },
+  progressTrack: {
+    height: 3,
+    backgroundColor: DARK.SURFACE,
+    marginHorizontal: LAYOUT.SCREEN_PADDING,
+    borderRadius: 2,
+    overflow: 'hidden',
+  },
+  progressFill: {
+    height: '100%',
+    backgroundColor: BRAND.PRIMARY,
+    borderRadius: 2,
+  },
+  content: {
+    flex: 1,
+    paddingHorizontal: LAYOUT.SCREEN_PADDING,
+    paddingTop: SPACING[8],
+  },
+})