v0.0.1 of dartstream_client

Public Dart client for wiring Flutter, Flame, and server apps to DartStream SaaS. Changelog excerpt: - Initial public DartStream SaaS client surface. - Add named workflow clients for auth, platform, experience, reactive, persistence, and billing. - Add production, development, and local service URL presets. - Add authenticated generic JSON request helpers for routes that are not yet wrapped by typed convenience methods. - Add billing checkout, portal, subscription, and feature-check helpers. - Add persistence provider catalog and connection-test helpers. - Preserve game-oriented cloud save, inv[...]