feat: add EAS build config and app store asset structure (FRE-4572)

- Create eas.json with development, preview, and production build profiles
- Add submit configuration for iOS App Store and Google Play
- Create app store metadata with listing copy, keywords, and requirements
- Add screenshot capture guides for iOS and Android
- Add marketing asset directory structure

packages/mobile/assets/store/marketing/README.md

@@ -0,0 +1,11 @@
+# Marketing Assets
+
+Place marketing materials here.
+
+## Required
+- `app-store-preview.png` - 1200x628 OG image for social sharing
+- `feature-graphic.png` - 1024x500 for Google Play feature graphic
+
+## Optional
+- `promo-video.mp4` - 30s promo for app store video preview
+- `press-kit.zip` - Press kit with logos, screenshots, and brand guidelines