Add @trails-cool/api package with Zod schemas for REST API contract
Single source of truth for the Journal REST API:
- API_VERSION semver constant (1.0.0)
- Endpoint path constants (routes, activities, auth, uploads, push)
- Zod schemas for all request/response shapes:
- Routes: list, detail, create, update, compute
- Activities: list, detail, create
- Auth: token exchange, refresh, device management
- Discovery: instance info + API version
- Uploads: presigned URL flow
- Errors: structured error response with field-level details
- Cursor-based pagination schemas
- TypeScript types inferred from Zod (z.infer)
Used by Journal server (validation) and mobile client (type safety).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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