Redesign onboarding flow: new Stitch-inspired UI (3 screens)

Replace the 4-screen onboarding (Welcome → Calibrate → Connect → Goal) with a
3-screen lab-themed flow (The Basics → Connect Devices → Choose Goal) based on
Google Stitch designs.

Key changes:
- Remove Welcome screen (now redirects to calibrate)
- New design system: Space Grotesk + Inter fonts, Material 3 color tokens,
  light/dark adaptive theme, atmospheric gradient backgrounds
- Screen 1 (The Basics): 3 biological sex options (male/female/other) with
  icons, underline-styled DOB inputs, lab motif decorative element
- Screen 2 (Connect Devices): 2-column card grid with device logos, category
  sections (Wearables + CGMs), status badges
- Screen 3 (Choose Goal): Rich goal cards with category labels, descriptions,
  watermark icons, asymmetric 2-column stagger layout
- Consistent header (Health Decoder brand + step indicator) across all screens
- Gradient CTA buttons, back navigation on screens 2-3
- DB migration to allow 'other' biological sex value
- Update UserProfile type and downstream consumers for 'other' sex option
- 31 onboarding tests + updated index redirect test (37 total)

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

Author: schwaaamp

mobile/assets/images/providers/fitbit-logo.png

@@ -30,6 +30,8 @@
   "dependencies": {
     "@evennit/notifee-expo-plugin": "^3.8.0",
     "@expo-google-fonts/dev": "^0.4.7",
+    "@expo-google-fonts/inter": "^0.4.2",
+    "@expo-google-fonts/space-grotesk": "^0.4.1",
     "@expo/ngrok": "4.1.3",
     "@expo/vector-icons": "^15.0.2",
     "@gorhom/bottom-sheet": "5.2.6",