dsh-calendar: A CalDAV and Chinese Calendar Integration Plugin for DeepSeek Harness

`johnxu22786/calendar` is a standalone plugin for DeepSeek Harness (DSH), designed specifically to address calendar integration and Chinese calendar features. It supports the standard CalDAV protocol, with automatic discovery and Basic/OAuth2 authentication; it includes an RFC 5545 recurring-rule engine implemented from scratch, supporting single-instance editing and conflict detection. For Chinese users, the plugin provides lunar-calendar conversion, Chinese holidays, sexagenary-cycle support, and time-zone features. It has no runtime dependencies, is installed via npm, and supports secure authentication methods such as the Google OAuth2 device flow.