v0.1.0 of presence_sdk

Dart SDK for the Presence realtime platform. Drop-in chat, notifications, and live presence with WebSocket fan-out and automatic reconnection. Changelog excerpt: - Initial release - PresenceClient.connect()— connect with a custom token provider - PresenceClient.connectWithCredentials()— connect with client ID + secret (two-step auth handled automatically) - ChatModule— conversations, messages, reactions, read receipts, typing indicators - NotificationsModule— publish, inbox, mark read, live notification stream - PresenceModule— watch subjects, online/offline events, heartbeat - Automatic WebSocket reconnection with exponential backoff + jitter [...]