Add comprehensive test suite and improve Expo integration

[andyfischer]

Summary

This PR adds a complete test suite for the prism-framework-expo package and improves the Expo integration with better documentation, error handling, and developer experience features.

Key Changes

Testing Infrastructure

• Added vitest configuration and test suite covering:
  • ExpoSqliteDatabase — database operations (get, list, run, close, schema initialization)
  • ExpoEventEmitter — event subscription/publishing with proper cleanup
  • createExpoFetch — endpoint routing, parameter handling, error normalization
  • expoLaunch — app initialization, database setup, middleware warnings, job startup
  • usePrismApp — React hook for async initialization with loading/error states
  • Full integration test with real SQLite operations via better-sqlite3 mock

Core Improvements

• Database Injection: expoLaunch() now accepts pre-created ExpoSqliteDatabase instances, allowing endpoints to close over the same database reference (fixes a critical pattern for mobile apps)
• Error Handling Parity: HttpError exceptions from callEndpoint() are now normalized to match webFetch error format ("Fetch error, status: N")
• Request Context: createExpoFetch() now wraps calls in withRequestContext() so endpoints can access auth via getCurrentRequestContext()
• Auth Support: Added getAuth option to both expoLaunch() and createExpoFetch() for providing authorization data on each request
• Migration Support: Added migrateSchema() method to ExpoSqliteDatabase for tracking applied migrations (safer for app updates)

New Exports

• ExpoEventEmitter — in-process event emitter (mobile equivalent of SSE)
• usePrismApp — React hook for managing async initialization in Expo layouts
• Authorization re-exported from core for mobile auth patterns

Documentation & Examples

• Updated creating-mobile-apps.md with modern patterns (database injection, React hooks, auth)
• Updated README.md with clearer setup examples and API documentation
• Added sample Expo app structure:
  • _layout.tsx — demonstrates usePrismApp hook integration
  • prismSetup.ts — app and database initialization
  • notesService.ts — platform-agnostic service with database access
  • NotesScreen.tsx — React Native component using apiFetch

Implementation Details

• ExpoEventEmitter uses Map<string, Set<callback>> for efficient key-based event routing with automatic cleanup
• ExpoSqliteDatabase.migrateSchema() uses SHA-256 hashing of statements to track migrations
• Test suite includes a createExpoSQLiteMock() wrapper around better-sqlite3 to simulate expo-sqlite's synchronous API
• All tests use vitest with proper cleanup (temp directories, database connections)

Breaking Changes

None — all changes are additive or improve existing behavior.

https://claude.ai/code/session_0181oRm3itxnkB6WVZMjer4U