Add Expo/React Native mobile prototype for iOS, Android, and web

[srctl]

This PR introduces a complete Expo (SDK 57, React Native 0.86) prototype of the Roost mobile application, enabling evaluation of React Native viability against the existing SwiftUI implementation.

Summary

A new apps/mobile-expo application that ports four core screens from the SwiftUI app (apps/ios) to run on iOS, Android, and web platforms. The prototype connects to the same /api/mobile/v1 API using device tokens, allowing it to run against a real Roost server or the native UI fixture.

Key Changes

• Connect Screen: Server and token validation, session/agents check, secure storage via expo-secure-store (Keychain on iOS, SecureStore on Android, localStorage on web)
• Agents Screen: Native large-title list with search, pull-to-refresh, and 15-second foreground refresh polling
• Chat Screen: Full conversation management with revision-based polling (1s busy / 4s idle / 8s error), idempotent message sending with retry, stop functionality, approval cards, reply threads, and swipe-to-reply gestures
• Feed Screen: Story list with filtering (all/saved), pull-to-refresh, and native reader sheet
• API Layer (lib/api.ts): Complete port of the Swift API client with bearer token auth, error handling, and user-facing error messages
• Conversation State (lib/conversation.ts): Revision-based polling, pending payload reuse after network failures, and message deduplication
• Session Management (lib/session.tsx): Secure connection storage and agent list caching
• UI Components:
  • Typing indicator with staggered dot animation
  • Message composer with glass effect (iOS 26+) and attachment placeholder
  • Message rows with swipe-to-reply, context menus, and markdown rendering
  • Native buttons using SwiftUI on iOS, Material Design on Android/web
  • Character pixel art renderer (shared with SwiftUI app)
  • Markdown parser supporting headings, lists, code blocks, and inline formatting
• Theme System: Shared color palette with the SwiftUI app via Themes.json
• Keyboard Handling: Keyboard-aware chat scrolling that lifts content only when newest message is visible
• Animations: React Native Reanimated for smooth transitions, spring physics, and gesture-driven interactions

Notable Implementation Details

• Platform-specific code uses .ios.tsx and .tsx suffixes for SwiftUI integration on iOS while maintaining Android/web compatibility
• Shared JSON resources (Characters.json, Themes.json) imported from the iOS app via Metro config
• Gesture handling with react-native-gesture-handler for swipe-to-reply with haptic feedback
• Secure token storage with platform-appropriate backends (Keychain, SecureStore, localStorage)
• Comprehensive TypeScript types matching the Swift API models
• Accessibility labels and roles throughout for screen reader support

https://claude.ai/code/session_01N4Td1Sf9cr1ZvAJ3uowaNJ