Implement OAuth2 PKCE auth, discovery, and mobile API client

Journal server (Phase 1.4 + 1.5):
- Add oauth_clients, oauth_codes, oauth_tokens tables to journal schema
- Implement GET /oauth/authorize with PKCE flow and login redirect
- Implement POST /oauth/token (authorization_code + refresh_token grants)
- Add validateBearerToken() + getAuthenticatedUser() middleware
- Seed trails-cool-mobile as trusted OAuth client on server startup
- Add GET /.well-known/trails-cool discovery endpoint
- Add returnTo support to login page and magic link verify
- Add @trails-cool/api workspace dependency to journal

Mobile app (Phase 1.5 + 1.6):
- Login screen with server URL input and discovery validation
- OAuth2 PKCE login via expo-web-browser with expo-crypto for Hermes
- Token storage in expo-secure-store with auto-refresh on 401
- API client with bearer token injection and typed errors
- Server URL persistence with localhost default in dev mode
- API version compatibility check on app foreground
- Log out + switch server on Profile tab
- iOS ATS exception for local networking

Tests:
- PKCE crypto verification, OAuthError, token generation
- Discovery endpoint response shape
- API version semver compatibility
- API client error types

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

apps/journal/package.json

@@ -18,6 +18,7 @@
     "@sentry/react": "catalog:",
     "@simplewebauthn/browser": "^13.3.0",
     "@simplewebauthn/server": "^13.3.0",
+    "@trails-cool/api": "workspace:*",
     "@trails-cool/db": "workspace:*",
     "@trails-cool/gpx": "workspace:*",
     "@trails-cool/i18n": "workspace:*",