feat: onboarding flow (6 screens) + audio engine + design system

Onboarding:
- 6-screen flow: Problem → Empathy → Solution → Wow → Personalization → Paywall
- useOnboarding hook with Zustand + AsyncStorage persistence
- MiniTimerDemo with live 20s timer + haptics
- Auto-redirect for first-time users
- Mock RevenueCat for dev testing

Audio:
- useAudioEngine hook with expo-av
- Phase sounds (count_3/2/1, beep, bell, fanfare)
- Placeholder music tracks

Design System:
- Typography component + constants
- GlassView component
- Spacing, shadows, animations, borderRadius constants
- Extended color palette (phase gradients, glass, surfaces)

Timer:
- Fix: handle 0-duration phases (immediate advance)
- Enhanced TimerDisplay with phase gradients

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

package.json

@@ -12,15 +12,19 @@
   },
   "dependencies": {
     "@expo/vector-icons": "^15.0.3",
+    "@react-native-async-storage/async-storage": "^2.2.0",
     "@react-navigation/bottom-tabs": "^7.4.0",
     "@react-navigation/elements": "^2.6.3",
     "@react-navigation/native": "^7.1.8",
     "expo": "~54.0.33",
+    "expo-av": "~16.0.8",
+    "expo-blur": "~15.0.8",
     "expo-constants": "~18.0.13",
     "expo-font": "~14.0.11",
     "expo-haptics": "~15.0.8",
     "expo-image": "~3.0.11",
     "expo-keep-awake": "~15.0.8",
+    "expo-linear-gradient": "~15.0.8",
     "expo-linking": "~8.0.11",
     "expo-router": "~6.0.23",
     "expo-splash-screen": "~31.0.13",
@@ -36,13 +40,14 @@
     "react-native-safe-area-context": "~5.6.0",
     "react-native-screens": "~4.16.0",
     "react-native-web": "~0.21.0",
-    "react-native-worklets": "0.5.1"
+    "react-native-worklets": "0.5.1",
+    "zustand": "^5.0.11"
   },
   "devDependencies": {
     "@types/react": "~19.1.0",
-    "typescript": "~5.9.2",
     "eslint": "^9.25.0",
-    "eslint-config-expo": "~10.0.0"
+    "eslint-config-expo": "~10.0.0",
+    "typescript": "~5.9.2"
   },
   "private": true
 }