Implement Weibo private message platform via the Open IM WebSocket protocol (open-im.api.weibo.com). Supports app_id/app_secret auth, automatic token refresh, heartbeat keep-alive, reconnect with exponential backoff, message dedup, and chunked sending for long messages (2000 char limit). Includes plugin registration, build tag (no_weibo), unit tests, setup documentation, and cross-references in all platform docs. Made-with: Cursor