remove: 移除 Agent 创建群聊的 SDK 方法和相关描述

完善文档

fix: handle group removal gracefully to prevent 403 errors

feat: add update_group method to rename groups

feat: add DM routing to prevent agent from creating groups when messaging friends

feat: add file upload to SDK and fix reply() attachments support

docs: update README to reflect current features and remove always mode

feat: add contact ability and refactor Gateway config strategy

init